Ion injector and lens system for ion beam milling

ABSTRACT

The embodiments herein relate to methods and apparatus for performing ion etching on a semiconductor substrate, as well as methods for forming such apparatus. In some embodiments, an electrode assembly may be fabricated, the electrode assembly including a plurality of electrodes having different purposes, with each electrode secured to the next in a mechanically stable manner. Apertures may be formed in each electrode after the electrodes are secured together, thereby ensuring that the apertures are well-aligned between neighboring electrodes. In some cases, the electrodes are made from degeneratively doped silicon, and the electrode assembly is secured together through electrostatic bonding. Other electrode materials and methods of securing may also be used. The electrode assembly may include a hollow cathode emitter electrode in some cases, which may have a frustoconical or other non-cylindrical aperture shape. A chamber liner and/or reflector may also be present in some cases.

BACKGROUND

Fabrication of semiconductor devices typically involves a series ofoperations in which various materials are deposited onto and removedfrom a semiconductor substrate. One technique for material removal ision beam etching, which involves delivering ions to the surface of asubstrate to physically and/or chemically remove atoms and compoundsfrom the surface in an anisotropic manner. The impinging ions strike thesubstrate surface and remove material through momentum transfer (andthrough reaction in the case of reactive ion etching).

SUMMARY

Various embodiments herein relate to methods and apparatus forperforming ion beam etching to remove material from a substrate. Certainembodiments relate to methods for forming an electrode assembly used inan ion beam etching application. Other embodiments relate to theelectrode assemblies formed by such methods. Many different embodimentsare presented herein. The various features of the different embodimentsmay be combined as desired for a particular application.

In one aspect of the disclosed embodiments, a method of making anelectrode assembly for use in an ion beam etching reactor is provided,the method including: providing a first electrode, a second electrodeand a third electrode; providing and securing a first inter-electrodestructure such that it is immobilized between the first electrode andthe second electrode, and providing and securing a secondinter-electrode structure such that it is immobilized between the secondelectrode and the third electrode, where the first electrode, secondelectrode, third electrode, first inter-electrode structure, and secondinter-electrode structure are substantially vertically aligned with oneanother to form the electrode assembly; and forming a plurality ofapertures in the first electrode, second electrode and third electrodewhile the first inter-electrode structure and the second inter-electrodestructure are immobilized in the electrode assembly.

In some embodiments, the first electrode, second electrode, and thirdelectrode include degeneratively doped silicon, where securing the firstinter-electrode structure includes attaching the first inter-electrodestructure to the first electrode and/or to the second electrode, andwhere securing the second inter-electrode structure includes attachingthe second inter-electrode structure to the second electrode and/or tothe third electrode. Electrostatic bonding may be used to create verygood connections between the relevant pieces in some cases. In otherembodiments, securing the first inter-electrode structure includesdepositing the first inter-electrode structure directly on the firstelectrode or the second electrode, and/or securing the secondinter-electrode structure includes depositing the second inter-electrodestructure directly on the second electrode or the third electrode. Incertain cases, securing the first inter-electrode structure includesproviding adhesive or a glass frit to secure the first inter-electrodestructure between the first electrode and the second electrode, and/orsecuring the second inter-electrode structure includes providingadhesive or a glass frit to secure the second inter-electrode structurebetween the second electrode and the third electrode. In someimplementations, securing the first inter-electrode structure andsecuring the second inter-electrode structure includes forming two ormore guide holes in each of the first electrode, second electrode, andthird electrode, and inserting pins through the guide holes. In these orother cases, securing the first inter-electrode structure and securingthe second inter-electrode structure includes providing brackets orclamps that directly or indirectly secure the first inter-electrodestructure and the second inter-electrode structure and that directlysecure at least the first electrode and the third electrode. The firstinter-electrode structure and/or the second inter-electrode structuremay be a continuous layer of material before forming the apertures insome cases.

In some embodiments, forming apertures in first electrode, secondelectrode and third electrode further includes forming apertures in thefirst inter-electrode material and in the second inter-electrodematerial. The method may further include after forming the apertures,immersing the electrode assembly in etching solution to thereby etch andremove at least a portion of the first inter-electrode layer and aportion of the second inter-electrode layer. Immersing the electrodeassembly in etching solution may result in the formation of supportstructures in contact with either the first electrode and the secondelectrode, or in contact with the second electrode and the thirdelectrode, the support structures being formed from the firstinter-electrode structure and the second inter-electrode structure. Thefirst, second, and third electrodes may be shaped, before and/or afterforming the apertures, to prevent the electrodes from bowing.

Further, the first, second, and third electrodes and the first andsecond inter-electrode structures may have coefficients of thermalexpansion (CTE) that differ from one another by about 50% or less. Inother cases the CTEs match even more closely. In some cases, dust isremoved from between the first and second electrode and/or from betweenthe second and third electrodes, after forming the apertures. Theapertures may be drilled with a laser in certain cases, for example aQ-switched CO₂ laser, a pulsed UV laser, or a diode pumped solid-statelaser (DPSS). Another process for forming the apertures includespositioning one or more metal structures on the first electrode; placingthe electrode assembly in an electrolytic bath; and applying an electricfield to thereby cause the metal structure(s) to form one or moreapertures in the first electrode, the first inter-electrode material,the second electrode, the second inter-electrode material, and the thirdelectrode. The method may further include before placing the electrodeassembly in the electrolytic bath, securing a reflector precursor layerto the third electrode, opposite the second inter-electrode structure;and after the one or more metal structures form the one or moreapertures in the third electrode, tilting the electrode assembly in theelectrolytic bath and continuing to apply the electric field to therebyform one or more apertures in the reflector precursor layer to form areflector, where the apertures in the third electrode are aligned withthe apertures in the reflector at an interface between the thirdelectrode and the reflector, and where the apertures do not provide adirect line of sight through the electrode assembly and reflector. Moregenerally speaking, in some cases, the method includes attaching areflector to the third electrode, where the reflector blocks a directline-of-sight through the electrode assembly.

In certain cases, the electrodes are fabricated to include apertureshaving different diameters for the different electrodes. For instance,the third electrode may have an aperture diameter that is larger thanthe aperture diameter of the second electrode (e.g., up to about 30%larger). Similarly, the second electrode may have an aperture diameterthat is larger than the aperture diameter of the first electrode (e.g.,up to about 30% larger). In certain embodiments, the apertures in one ormore of the electrodes have a taper of about 10° or less.

Gas pathways may be formed in the first inter-electrode structure and/orin the second inter-electrode structure. The gas pathways may allow gasto escape outwards from an interior region of the electrode assemblyduring etching.

In certain embodiments, before or after forming the apertures, a fourthelectrode may be provided to the electrode assembly, the fourthelectrode being provided above the first electrode, where the fourthelectrode forms a hollow cathode emitter electrode having a plurality ofhollow cathode emitters. The hollow cathode emitter electrode may havean upper surface and a lower surface, the lower surface facing the firstelectrode. In various cases, before, during, or after forming theapertures in the first, second, and third electrodes, a plurality ofholes may be formed in the hollow cathode emitter electrode, each holehaving a diameter that is larger at the upper surface and smaller towardthe lower surface, where the holes are aligned with a position of theapertures after the apertures are formed in the first, second, and thirdelectrodes. The hollow cathode emitters of the hollow cathode emitterelectrode may have various shapes. In certain cases, the holes in thehollow cathode emitter electrode include a lower cylindrical portion andan upper variable diameter portion. The upper variable diameter portionmay have a funnel shape. In certain similar embodiments, the firstelectrode may be fabricated as a hollow cathode emitter electrode havingany of the properties described with respect to the hollow cathodeemitter electrode.

Various embodiments herein relate to methods and apparatus forperforming ion beam etching. These embodiments may utilize an electrodeassembly fabricated according to the disclosed techniques. However, suchelectrode assemblies are not necessarily present in all embodiments.

For instance, in another aspect of the disclosed embodiments, a methodof etching a semiconductor substrate is provided, the method including:positioning a substrate on a substrate support, wherein a rotationmechanism coupled to the substrate support is configured to rotate thesubstrate at an accuracy of about 2° or better; applying a first bias toa first electrode and a second bias to a second electrode, where thefirst and second electrodes include apertures therein, and supplyingplasma above the first and second electrodes, where ions pass throughthe apertures in the first and second electrodes toward a surface of thesubstrate; while supplying the plasma, cyclically rotating the substrateand substrate support in a first direction and in a second directionthat is opposite the first direction; and etching the substrate as aresult of ions or particles impacting the surface of the substrate whilethe substrate is rotated.

The rotations are limited by the configuration of the substrate support.In other words, the substrate may rotate about 215° or less from acentral starting position in the first direction, and rotate about 215°or less from the central starting position in the second direction.Because the substrate begins the rotation in the second direction froman end point of the rotation in the first direction, the rotation in thesecond direction may be about 430° or less overall. Likewise, once thesubstrate rotates in the first direction again, the rotation starts froman end point of the rotation in the second direction, and thus, thesecond (or n^(th)) rotation in the first direction may be about 430° orless. In some cases, the substrate holder is configured to rotate about±180° or less. Such a configuration may permit substrate rotations ofabout 360° in either direction as measured from the central measuringpoint.

Different rates of rotation may be used during different portions of therotations. For instance, the substrate may rotate at a first averagerotation rate when rotating in the first direction, and at a secondaverage rotation rate when rotating in the second direction, the firstand second average rotation rates being different. In another example,the substrate rotations in each direction may include a slower portionand a faster portion. The ions or particles may impact the surface ofthe substrate during only a portion of the rotations. For instance, theions or particles may impact the surface of the substrate when thesubstrate rotates in the first direction but not when the substraterotates in the second direction. Similarly, the ions or particles mayimpact the surface of the substrate during the slower portion of arotation but not during the faster portion of a rotation.

In various embodiments, the substrate holder is configured to rotateand/or tilt the substrate at an accuracy of about 2° or better. Suchaccuracy is particularly beneficial where the substrate rotates in twodifferent directions. The method may include impacting the ions on areflector positioned below the second electrode, thereby neutralizingthe ions to form the particles. The method may also include passing ionsthrough apertures in a third electrode positioned below the secondelectrode. The third electrode may be grounded. The third electrode maybe positioned above the reflector in cases where both elements arepresent. In some embodiments, the method further includes generating aplurality of micro jet plasma discharges in a plurality of hollowcathode emitters in a hollow cathode emitter electrode positioned abovethe first and second electrodes, where the micro jet plasma dischargesare aligned with the apertures in the first and second electrodes.

The rotation patterns described with regard to the previous embodimentsmay be utilized in any of the etching and etching apparatus embodimentsdisclosed herein. However, such rotation patterns (i.e., cyclicbi-directional rotation) are not needed in every embodiment. Otherembodiments may be configured to utilize continuous rotation in a singledirection, for example.

In another aspect of the disclosed embodiments, a method of etching asemiconductor substrate is provided, the method including: providing asubstrate to a reaction chamber including: a first electrode, a secondelectrode, and a third electrode, each electrode having a plurality ofapertures formed therein, where the apertures are formed after the firstelectrode, second electrode, and third electrode are immobilized withrespect to one another in an electrode assembly, and where the aperturesare formed in the first electrode, the second electrode, and the thirdelectrode in a single operation, a substrate support, and one or moregas inlets; generating or supplying plasma above the first electrode;applying a first bias to the first electrode and applying a second biasto the second electrode to thereby direct ions toward the substrate incollimated ion beams; and etching the substrate as a result of the ionsbeing directed toward the substrate.

As noted above, the electrode assembly may be formed through any of theassembly formation methods discussed herein.

The method may further include impacting the ions on a reflectorpositioned below the third electrode to thereby neutralize the ions andprovide a neutral beam. In certain implementations, the method includescyclically rotating the substrate in a first direction and in a seconddirection opposite the first direction. The substrate support may beconfigured to move about ±215° or less, for example about ±180°, orbetween about ±180° and ±215°. The reaction chamber may further includea shutter that is configured to prevent the ions from impinging upon thesubstrate when the shutter is closed. The shutter may prevent ions fromimpinging upon the substrate while the substrate is rotated in aparticular direction. In these or other cases, the shutter may preventions from impinging upon the substrate during a particular portion ofeach rotation (e.g., blocking ions when the substrate rotates during afaster portion and not blocking the ions when the substrate rotatesduring a slower portion of the rotation). In some cases, rotating thesubstrate includes rotating the substrate at a first average speed inthe first direction and at a second average speed in the seconddirection, the first average speed being different from the secondaverage speed.

The method may further include tilting the substrate during etching.Such tilting may result in collimated ion beams or particle beamsimpacting the substrate at a non-normal angle. As noted with respect tocertain other aspects of the disclosed embodiments, the reaction chambermay further include a fourth electrode above the first electrode, wherethe fourth electrode is a hollow cathode emitter electrode having aplurality of hollow cathode emitters. In such cases, generating plasmaabove the first electrode may include generating plasma in the hollowcathode emitters. Such plasma generation may be in addition to plasmageneration that occurs above the hollow cathode emitter electrode.Generating plasma in the hollow cathode emitters may include applying anRF bias to the hollow cathode emitter electrode. In certain cases, themethod further includes generating a pressure differential of about 1Torr or greater above vs. below the hollow cathode emitter electrode. Insome embodiments, a gas conductance through the hollow cathode emitterelectrode is about 800 L/min or less.

In another aspect of the disclosed embodiments, an apparatus for etchinga semiconductor substrate is provided, the apparatus including areaction chamber including: an ion source configured to expose thesubstrate with a flux of ions or neutral particles generated from theions; a substrate support configured to support the substrate duringetching; a rotation mechanism for tilting and rotating the substrate andsubstrate support, the rotation mechanism configured to rotate and tiltthe substrate each at an accuracy of about 2° or better; and acontroller having instructions to set a substrate tilt angle, rotationangle, and ion energy during etching. The substrate support may beconfigured to rotate about ±215° or less, for example ±180°, withrespect to a central starting position at 0°. In some embodiments, therotation mechanism includes a sensor, stepper, or other mechanism thatcan detect a rotational position of the substrate at an accuracy ofabout 2° or better. In certain cases the ion source includes a pluralityof electrodes secured together into an electrode assembly as describedherein. Further, the apparatus may include a hollow cathode emitterelectrode having a plurality of hollow cathode emitters therein.

In yet another aspect of the disclosed embodiments, an apparatus foretching a semiconductor substrate is provided, the apparatus including:a reaction chamber; a substrate support; an inlet for supplying one ormore gases or plasma to the reaction chamber; a first electrode, asecond electrode, and a third electrode, each having a plurality ofapertures therein, where the second electrode is positioned below thefirst electrode and the third electrode is positioned below the secondelectrode; a hollow cathode emitter electrode having a plurality ofhollow cathode emitters, where the hollow cathode emitters are alignedwith the apertures in the first, second, and third electrodes, and wherethe hollow cathode emitter electrode is positioned above the firstelectrode; and one or more RF sources configured to do one or more of(i) generate a plasma above the hollow cathode emitter electrode, (ii)apply a bias to the hollow cathode emitter electrode, (iii) apply a biasto the first electrode, and/or (iv) apply a bias to the secondelectrode.

In some embodiments, the one or more RF sources are configured to dothree or more of (i)-(iv), for example all of (i)-(iv). The apparatusmay further include a rotation mechanism configured to rotate thesubstrate and substrate support with an accuracy of about 2° or better.The apparatus may further include a controller having instructions tocontrol a tilt angle, rotation angle, and ion energy during etching.Further, the apparatus may include a reflector positioned below thethird electrode, where the reflector is operable to neutralize ionspassing through the apertures in the first, second, and third electrodesduring etching.

In certain cases, the electrodes include apertures having differentdiameters for the different electrodes. For instance, the thirdelectrode may have an aperture diameter that is larger than the aperturediameter of the second electrode (e.g., up to about 30% larger).Similarly, the second electrode may have an aperture diameter that islarger than the aperture diameter of the first electrode (e.g., up toabout 30% larger). In certain embodiments, the apertures in one or moreof the electrodes have a taper of about 10° or less. The gas conductancethrough the hollow cathode emitters may be fairly low, for example about800 L/min or less when a gas flow rate of about 1 SLM is provided abovethe hollow cathode emitter electrode.

In another aspect of the disclosed embodiments, an apparatus for etchinga substrate is provided, the apparatus including: a reaction chamberincluding: a substrate holder configured to support a substrate duringetching, one or more inlets for providing gas phase reactants and/orplasma to the reaction chamber, an electrode assembly comprising a firstelectrode, a second electrode, and a third electrode, each electrodecomprising a plurality of apertures, where the apertures of eachelectrode are formed in a single process including: securing the firstelectrode, second electrode and third electrode together such that theyare vertically stacked and immobilized with respect to one another, andafter securing the first electrode, second electrode and third electrodetogether, forming the apertures in the first electrode, secondelectrode, and third electrode such that the apertures in each electrodeare aligned.

The first, second, and third electrode may be secured to one another inan electrode assembly. The electrode assembly may be formed through anyof the disclosed methods. In some cases, at least one of the firstelectrode, second electrode, and third electrode has a thickness betweenabout 0.5 mm-10 cm, or between about 1 mm-3 cm, for example about 5 mm.The apertures may have a diameter between about 0.5-1 cm. Other aspectsof aperture dimensions are described herein.

In some cases, the electrodes are made from degeneratively dopedsilicon. In such cases, the first electrode may be secured to the secondelectrode via a first inter-electrode structure that iselectrostatically bonded to at least one of the first electrode and thesecond electrode, and the second electrode may be secured to the thirdelectrode via a second inter-electrode structure that iselectrostatically bonded to at least one of the second electrode and thethird electrode. In certain embodiments, at least one of the first andsecond inter-electrode structures include silicon oxide. At least one ofthe first and second inter-electrode structures may support the first,second, and/or third electrodes at or near their peripheries. In somecases, at least one of the first and second inter-electrode structuresincludes a ring and/or ribs. In certain implementations, the first,second, and third electrodes include a refractory metal.

The substrate holder may be configured to rotate ±215° or less duringetching, for example about ±180°. A controller may have instructions torotate the substrate and substrate holder cyclically in a firstdirection and a second direction opposite the first direction. Variablerotation speeds may be used during the rotations. A shutter may be usedto prevent ions and/or particles from impacting the substrate duringcertain portions of the rotations. In certain embodiments, a chamberliner may be used to cover interior surfaces of the reaction chamberduring etching, where the chamber liner includes a sputter-resistantmaterial.

These and other features will be described below with reference to theassociated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a simplified view of a reaction chamber used for etchingsemiconductor substrates.

FIG. 2 illustrates a cross-sectional view of an electrode assemblyaccording to certain embodiments.

FIG. 3 panels A-H show examples of various possible shapes that may beused for inter-electrode structures in an electrode assembly accordingto some embodiments.

FIG. 4 depicts a cross-sectional view of a portion of an inter-electrodestructure.

FIGS. 5A-5D illustrate steps in forming an electrode assembly accordingto certain implementations.

FIG. 6A illustrates a top-down view of an electrode having a number ofapertures omitted for the purpose of providing increased structuralsupport to the electrode assembly.

FIGS. 6B and 6C show cross-sectional views of an electrode assembly atdifferent points during formation using electrodes having the shapeshown in FIG. 6A.

FIGS. 7A-7D depict various ways of securing an electrode assemblytogether according to some embodiments.

FIG. 8 shows a close-up cross-sectional view of a hollow cathode emitterelectrode used in certain implementations.

FIG. 9 illustrates formation of micro jets in a frustoconically shapedaperture of a hollow cathode emitter electrode.

FIG. 10 shows a reaction chamber equipped with a reflector used toneutralize the ion beam in certain embodiments.

FIG. 11 shows two electrodes being secured together via aninter-electrode material using electrostatic bonding.

DETAILED DESCRIPTION

In this application, the terms “semiconductor wafer,” “wafer,”“substrate,” “wafer substrate,” and “partially fabricated integratedcircuit” are used interchangeably. One of ordinary skill in the artwould understand that the term “partially fabricated integrated circuit”can refer to a silicon wafer during any of many stages of integratedcircuit fabrication thereon. A wafer or substrate used in thesemiconductor device industry typically has a diameter of 200 mm, or 300mm, or 450 mm. The following detailed description assumes the inventionis implemented on a wafer. However, the invention is not so limited. Thework piece may be of various shapes, sizes, and materials. In additionto semiconductor wafers, other work pieces that may take advantage ofthis invention include various articles such as printed circuit boards,magnetic recording media, magnetic recording sensors, mirrors, opticalelements, electro-optical devices, micro-mechanical devices and thelike.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the presented embodiments.The disclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Ion beam etching is commonly used in fabrication of semiconductordevices. As mentioned above, ion beam etching involves removing materialfrom the surface of a substrate by delivering energetic ions to thesubstrate surface. Ion beam etching may be broadly categorized intoprocesses that solely involve inert ions (e.g., argon ions), andprocesses that involve reactive ions or chemical reactions initiated byions (e.g., oxygen ions, certain ionized compounds such asfluorine-containing ionized compounds, reactive or inert ions initiatinga chemical reaction with a reactant chemisorbed or physisorbed on thesurface on the substrate, etc.). In these of processes, ions impinge onthe substrate surface and remove material through either direct physicalmomentum transfer (sputtering) or a chemical reaction initiated by theenergy transfer from the ions (reactive ion beam etching or chemicallyassisted ion beam etching). Reactive ion beam etching (RIBE) typicallyinvolves utilization of an ion that can chemically react with thesubstrate (such as oxygen, fluorine and the like). In chemicallyassisted ion beam etching (CAIBE), an inert ion either initiates achemical reaction between the substrate and a reactant (such as anapplied gas that is adsorbed on the surface), or generates a reactivesite on the surface of the substrate that reacts with an appliedreactant coincident with or subsequent to the generation of the reactantsite, or any combination thereof.

Certain applications for ion beam etching processes relate to etching ofnon-volatile materials. In some cases, the material etched is aconductive material. In certain embodiments, the material is etched inthe context of forming a magnetoresistive random-access memory (MRAM)device, a spin-torque-transfer memory device (STT-RAM), a phase-changememory device (PSM), a non-volatile conductor (copper, platinum, gold,and the like). In other applications, the ability to control the ionincident angle to the substrate can be useful in generating 3D devicessuch as vertically stacked memory.

When performing ion beam etching processes, it is desirable to promote ahighly uniform ion flux over the substrate surface. A high degree ofuniformity is beneficial in creating reliable devices across the entiresurface of the substrate. Further, it may be desirable in certain casesto promote a high ion flux and/or a high flux of a gas phase reactant.High flux can help maximize throughput. Another factor that affects thequality of the etching results is the ability to control the energy andangle at which the ions impact the surface. These factors are importantin forming features having desired dimensions and profiles.

FIG. 1 presents a simplified cross-sectional view of an apparatus 100for performing ion beam etching according to certain methods. In thisexample, substrate 101 rests on substrate support 103, which may beequipped with hardware (not shown) to provide electrical and fluidicconnections. The electrical connections may be used to supplyelectricity to the substrate support 103 or to an electrostatic chucklocated on or within the substrate support 103 (not shown) in somecases, while the fluidic connections may be used to provide fluids usedto control the temperature of the substrate 101 and substrate support103. The substrate support 103 may be heated by a heater (not shown) orcooled by a cooling mechanism (not shown). The cooling mechanism mayinvolve flowing cooling fluids through piping in or adjacent thesubstrate support 103. The substrate support 103 may be capable ofrotating and tilting at variable speeds and angles, as indicated by thedouble headed arrows in FIG. 1.

A plasma generation gas is delivered to a primary plasma generationregion 105. The plasma generation gas is energized by a plasma source107. In the context of FIG. 1, the plasma source 107 is a coil that actsas an inductively coupled plasma source. Other sources such ascapacitively coupled sources, microwave sources or discharge sources maybe employed in appropriately designed reactors. Plasma forms in theprimary plasma generation region 105. An extraction electrode 109includes a series of apertures 110 through which ions are extracted.

The apertures 110 may have a diameter between about 0.5-1 cm, and aheight that is defined by the thickness of the electrode. The apertures110 may have a height to width aspect ratio (AR) between about0.01-100.0. In some cases the apertures 110 are arranged in a hexagonal,square grid, or spiral pattern, though other patterns may be used aswell. A center-to-center distance between neighboring apertures may bebetween about 1 mm-10 cm. The apertures may be configured to achieve anoverall open area (i.e., sum of the area of each aperture) that isbetween about 0.1%-95% of the surface area of the electrode whenconsidering only a single (top or bottom) face of the electrode. Forexample, an electrode having a diameter of 40 cm and 500 holes eachhaving a diameter of 1 cm will have an open area of about 31% (393 cm²open area divided by 1257 cm² total area). The apertures 110 may havedifferent diameters in different electrodes. In some cases, the aperturediameter is smaller in upper electrodes and larger in lower electrodes.In one embodiment, the apertures in a lower electrode 113 are largerthan the apertures in a focus electrode 111 (e.g., between about 0-30%larger). In these or other cases, the apertures in the focus electrode111 are larger than the apertures in the extraction electrode 109 (e.g.,between about 0-30% larger).

The bias V₁ applied to the extraction electrode 109 with respect to thesubstrate 101 acts to provide kinetic energy to the ion with respect tothe substrate. This bias is generally positive and can range betweenabout 20-10,000 volts or more. In certain cases the bias on theextraction electrode is between about 20-2,000 volts. Positive ions inthe plasma above extraction electrode 109 are attracted to the lowerelectrode 113 by the potential difference between electrodes 109 and113. Focus electrode 111 is added to focus the ions, and if needed,repel electrons. A bias V₂ on this electrode can be either positive ornegative with respect to the extraction electrode 109, but is generallybiased negatively. The bias potential of focus electrode 111 isdetermined by the lensing characteristics of the focusing electrode 111.Bias voltages on the focus electrode include positive voltages betweenabout 1.1× to 20× the potential V₁ on the extraction electrode, andnegative voltages having a magnitude between about 0.001× to 0.95× thepotential of V₁. Due to the different potentials applied to thedifferent electrodes, a potential gradient exists. The potentialgradient may be on the order of about 1000 V/cm. Example separationdistances between neighboring electrodes fall between about 0.1-10 cm,or for example about 1 cm.

After the ions leave the bottom of the grounded lower electrode 113,they travel in a collimated and focused beam if the focus electrode 111voltage is set to produce a collimated beam. Alternatively the beam canbe made divergent if the focus electrode voltage is adjusted to eitherunder- or over-focus the ion beam. The lower electrode 113 is groundedin many (but not all) cases. The use of a grounded lower electrode 113in combination with a grounded substrate 101 results in a substrateprocessing region 115 that is substantially field free. Having thesubstrate located in a field-free region prevents electrons or secondaryions generated by collisions between the ion beam with residual gases orwith surfaces in the reaction chamber from being accelerated towards thesubstrate, thereby minimizing the risk of causing unwanted damage orsecondary reactions.

Additionally, it is important to prevent the substrate 101 from chargingfrom the ion beam itself, or from ejected secondary electrons generatedduring the ion beam collision with the substrate. Neutralization istypically accomplished by adding a low energy electron source (notshown) in the vicinity of the substrate 101. Since the positive chargeon the ion and the ejected secondary electrons both charge the substratepositively, low energy electrons in the vicinity of the substrate can beattracted to the positively charged surface and can neutralize thischarge. Performing this neutralization is much easier in a field freeregion.

In some applications it may be desirable to have a potential differencebetween the lower electrode 113 and substrate 101. For example, if verylow energy ions are required, it is difficult to maintain awell-collimated beam at low energy over long distances due to mutualrepulsion of the positively charged ions (space-charge effects). Onesolution to this is to place a negative bias on the lower electrode 113with respect to substrate 101 (or conversely biasing substrate 101positively with respect to the lower electrode 113). This allowsextracting the ions at higher energy, then slowing them down as theyapproach the substrate.

In certain ion beam etching operations, one of the three electrodes maybe omitted. Where this is the case, there is less flexibility regardingthe energy at which ions are directed to the surface of the substrate.This limitation arises because in order for the ions to be focused anddirected as desired, a particular ratio of bias potentials should beapplied to the two electrodes. The ratio of bias potentials iscontrolled by the focusing characteristics and geometries of the twoelectrodes. As such, where a particular geometry is used and aparticular bias/electrical state is desired on the lower electrode(e.g., grounded), there is little or no flexibility in the bias appliedto the upper electrode. The result is that a reaction chamber using sucha setup is limited in the range of ion energy that may be imparted toions as they travel through the various electrodes. The introduction ofa third electrode allows the ions to be focused/directed as desired atmany different ion energies, as described above.

Each of the electrodes 109, 111, and 113 has a thickness, which may bebetween about 0.5 mm-10 cm, or between about 1 mm-3 cm, for exampleabout 5 mm. The electrodes 109, 111, and 113 may each be the samethickness, or they may have different thicknesses. Further, theseparation distance between the extraction electrode 109 and the focuselectrode 111 may be the same, greater, or less than the separationdistance between the focus electrode 111 and the lower electrode 113.Each electrode 109, 111, and 113 also has dimensions, which may be lessthan, equal to or greater than the dimensions of the substrate beingprocessed. In certain embodiments, the electrodes' dimensions are closeto that of the substrate or substrate support (e.g., within about 50%).

The electrodes 109, 111, and 113, may be circular, rectangular or otherpolygonal shape. In certain embodiments the electrodes are long andnarrow, wherein the long dimension is approximately equal to or greaterthan one dimension of the substrate, and the substrate is scanned in theorthogonal direction such that the ion beam strikes uniformly across thesubstrate surface when averaged over time.

The apertures 110 in the extraction electrode 109, focus electrode 111and lower electrode 113 may be precisely aligned with one another.Otherwise, ions will be aimed incorrectly, and the on-wafer etchingresults will be poor. For instance, if a single aperture in the focuselectrode 111 is misaligned, it may result in one area of the substrate101 becoming over-etched (where too many ions are directed) and anotherarea of the substrate 101 becoming under-etched (where no ions or toofew ions are directed). As such, it is desirable for the apertures to beas aligned with one another as much as possible. In various cases themisalignment between vertically adjacent electrodes is limited to about1% or less of the hole diameter (as measured by the distance of a linearshift in the position of the aperture as compared to the adjacentaperture).

Ion beam etching processes are typically run at low pressures. In someembodiments, the pressure may be about 100 mTorr or less, for exampleabout 1 mTorr or less, and in many cases about 0.1 mTorr or less. Thelow pressure helps minimize undesirable collisions between ions and anygaseous species present in the substrate processing region. In certaincases, a relatively high pressure reactant is delivered in an otherwiselow pressure ion processing environment. Apparatus for achieving suchprocessing methods are described in U.S. patent application Ser. No.14/458,161, filed Aug. 12, 2014, and titled “DIFFERENTIALLY PUMPEDREACTIVE GAS INJECTOR,” which is herein incorporated by reference in itsentirety.

Ion beam etching processes may be used for atomic layer etchingprocesses in some embodiments. Atomic layer etching methods are furtherdiscussed in the following U.S. patents, each of which is hereinincorporated by reference in its entirety: U.S. Pat. No. 7,416,989,titled “ADSORPTION BASED MATERIAL REMOVAL PROCESS”; U.S. Pat. No.7,977,249, titled “METHODS OF REMOVING SILICON NITRIDE AND OTHERMATERIALS DURING FABRICATION OF CONTACTS”; U.S. Pat. No. 8,187,486,titled “MODULATING ETCH SELECTIVITY AND ETCH RATE OF SILICON NITRIDETHIN FILMS”; U.S. Pat. No. 7,981,763, titled “ATOMIC LAYER REMOVAL FORHIGH ASPECT RATIO GAPFILL”; and U.S. Pat. No. 8,058,179, titled “ATOMICLAYER REMOVAL PROCESS WITH HIGHER ETCH AMOUNT.”

Electrode Material

Typically, the material used to construct the electrodes should be hightemperature compatible in order to accommodate the substantial heatingthat occurs in many ion milling processes. Typically, the electrodematerial should also be mechanically rigid such that the electrodes donot bend or bow to a substantial degree when installed in an ion millingapparatus. Less rigid materials may be supported by additional supportstructures as discussed below. In many conventional cases the electrodesare constructed from a refractory metal (e.g., tungsten, tantalum, andmolybdenum are typical). Unfortunately, physical sputtering of theelectrodes often results in heavy metal contamination in the devicesbeing fabricated. This contamination can deleteriously affect theperformance of the devices.

In certain embodiments herein, one or more (in some cases all) of theelectrodes are made from doped silicon (e.g., degenerately dopedsilicon). Intrinsic and lightly doped silicon may not be sufficientlyconductive to serve as an electrode. The silicon may be polycrystallineor single crystalline. The dopant may be arsenic, boron, phosphorus, ora combination thereof. The dopant may be present at aconcentration/composition of at least about 10²⁰ atoms/cm³, for examplebetween about 10²⁰-10²³ atoms/cm³, or between about 10²²-10²³ atoms/cm³.The electrodes may have a conductivity between about 0.1-0.01 Ω-cm.

Silicon has a low thermal expansion coefficient, meaning that it doesnot undergo significant volume expansion as the silicon is heated.Additionally, silicon is stable at high temperatures and has arelatively low sputter yield (e.g., about 0.2 for 200 eV Argon).Further, even when material does sputter off of the silicon electrodes,most semiconductor devices are less sensitive to silicon surfacecontamination compared to contamination from most metals. The siliconcan be of a single crystal or poly-crystalline or amorphous type or anycombination of these types. Further, silicon electrodes may befabricated together as an assembly in ways that the conventional metalelectrodes cannot, as discussed further below.

In certain embodiments, one or more of the electrodes are made from amaterial other than silicon. In other cases, one or more electrodes mayinclude tungsten, tantalum, molybdenum, niobium, rhenium, titanium,vanadium, chromium, zirconium, ruthenium, rhodium, hafnium, osmium,iridium, or a combination thereof. While silicon-based electrodesprovide certain benefits, their use is not required in all embodiments.

Structure and Fabrication of Electrode Assembly

In conventional ion beam milling apparatus, each electrode isindividually fabricated. Fabrication involves forming a plate ofmaterial and then forming apertures in the plate. The apertures in eachelectrode are placed such that they align with the apertures in theother electrodes. Optical alignment methods may be used to alignapertures between neighboring plates. Where apertures are not perfectlyaligned with one another, the ion trajectory through such apertures isskewed. Ions that travel along such a skewed trajectory will impact thesubstrate at an angle that is non-uniform compared to ions that passthrough aligned apertures. Where the misalignment is substantial, theions may be blocked entirely from passing through such misalignedapertures. The skewing and blocking of ion trajectories as the ions passthrough the electrodes result in non-uniform ion impingement on thewafer surface (in terms of both the impact angle and the flux), whichresults in non-uniform ion milling results. The number of individualapertures on a single electrode may range between about 1-20,000, forexample between about 10-5,000. Due to the large number of apertures andthe fact that three different electrodes are separately formed andaligned, it is easy to fabricate electrodes with misaligned holes.

An example fabrication technique will now be described. In certainembodiments herein, a different order of operations is used. First,undrilled electrodes are formed into an assembly. Next, a single unifiedprocess is used to form apertures in all the electrodes in the assembly.This fabrication scheme results in electrodes that produce extremelywell-aligned and uniform ion trajectories and flux. One reason thisfabrication scheme has been avoided in the past is that it is verydifficult to adequately secure and machine the electrodes together in away that is mechanically stable during the aperture formation process,which may involve laser drilling (e.g., with a CO₂, UV or DPSS laser).Due to this mechanical instability, electrodes may fracture or becomemisaligned during the aperture formation process.

In some embodiments, the use of silicon-based electrodes permits analternative method for securing the electrodes together in amechanically stable way. In particular, a silicon electrode can bebonded to an inter-electrode material such as silicon dioxide, which canbe bonded to another silicon electrode. In certain embodiments, thebonding is electrostatic bonding. Such bonding methods are sometimesreferred to as anodic bonding. This method may be used to produce anelectrode assembly having multiple electrodes separated from one anotherby inter-electrode layers or structures made of silicon dioxide oranother material. Electrostatic and other bonding/joining methods arediscussed further below.

FIG. 2 presents a cross-sectional view of an electrode assembly 200 thatincludes an extraction electrode 209, a focus electrode 211, and a lowerelectrode 213. In some embodiments the electrodes are degenerately dopedsilicon, as described above. In other embodiments, more conventionalelectrode materials are used. Adjacent electrodes are separated byinter-electrode structures 220. The inter-electrode structures may berings, grids, webs, ribs, etc. Example inter-electrode structures arefurther shown and described with relation to FIG. 3. The inter-electrodestructures 220 serve at least two main purposes. First, theinter-electrode structures 220 support the electrodes to maintain adistance of separation between them and provide structural rigidity tothe electrode assembly 200. Next, the inter-electrode structures 220attach/bond the electrodes together in a mechanically stable fashionsuch that the apertures 210 can be drilled into each electrode 209, 211,and 213 in a single unified process. This unified process ensures thatthe apertures 210 are perfectly aligned between adjacent plates, suchthat ion trajectories through the various apertures 210 are extremelyuniform in terms of impact angle and flux. FIG. 2 presents the electrodeassembly 200 after the apertures 210 have been drilled.

FIG. 3 presents top-down views of various possible inter-electrodestructures that may be used in an electrode assembly according tocertain embodiments such as the one presented in FIG. 2. As shown inpanels A-G of FIG. 3, many different shapes may be used. In panel A, asimple ring is used. In some cases, particularly where relativelythinner electrodes are used, a simple ring may be inadequate to preventbowing of the electrodes. An electrode that bows when installed will notfunction to effectively aim the ions onto the substrate as desired.Instead, the ion trajectories will be skewed. Therefore, in variousembodiments additional support (which may be the same material as thering) may be added to the inter-electrode structure. In panels B and C,for instance, radial supports are added. Any number of radial supportsmay be used. In panel D, the radial supports shown in panel B constitutethe entire inter-electrode structure and no peripheral ring is used.Similarly, the peripheral ring may be omitted from any of the designsshown in panels C, E, F, and H, as well. The inter-electrode structureshown in panel E includes two supports that form chords across aperipheral ring. Any number of chords may be used. The supports may alsobe curved or waved when viewed from above. In panel F, the supports havea corrugated shape when viewed from above. The corrugated (orcurved/waved) support may be configured to fit between apertures whenconsidering a single electrode. In panel G, the inter-electrodestructure is square shaped. The square structure may also be modified toinclude additional supports as shown in the other panels of FIG. 3. Inpanel H, a series of three concentric inter-electrode structures isused. Any number of individual inter-electrode structures may be usedbetween each set of electrodes. In a related embodiment, the concentricstructures may be attached to one another, for example by radialsupports. In such a case, the inter-electrode structure may resemble aspider web. One of ordinary skill in the art would understand that thestructures provided in FIG. 3 represent only a fraction of possiblestructures. Many modifications are available without departing from thecontemplated embodiments.

In various cases, the inter-electrode structures may be designed suchthat they do not block any apertures. This type of design may involvecarefully controlling where the inter-electrode structure is located toensure that the structure is not placed where apertures are to beformed. In other implementations, overlap of apertures andinter-electrode structures is not problematic because theinter-electrode structures are etched along with the electrodes duringaperture formation. In this case, any inter-electrode structure materialthat would block the apertures is no longer present after the aperturesare formed. Such processing methods are discussed further below.

The material used to make the inter-electrode structures can be anyrigid or somewhat rigid, moderate to high resistance material. Forexample, the inter-electrode structures may be made from silicon dioxide(e.g., fused silica, boro-silicate glass, leaded glass, etc.), or from aceramic (e.g., silicon carbide, silicon nitride, zirconia, alumina,cordierite, aluminum nitride, a cermet, a perovskite, a titanate, azirconate, lithium-alumino-silicate or combination thereof), amachinable ceramic such as Macor® available from Corning Inc. ofCorning, N.Y., or from a polymer such as an epoxy, polyimide, polyamide,etc.

The inter-electrode structure may have a height (sometimes referred toas a thickness) between about 0.5 mm-10 cm, for example between about0.5 mm-5 cm, or between about 0.7 mm-2 cm. The height/thickness of theinter-electrode structure defines the separation distance betweenadjacent electrodes. In various cases two inter-electrode structures areused. A first inter-electrode structure separates the extractionelectrode from the focus electrode, and a second inter-electrodestructure separates the focus electrode from the lower electrode. Thefirst and second inter-electrode structures may have the same heightsuch that the separation between each set of electrodes is equal. Inother cases, the inter-electrode structures may have unequal height suchthat the distance between the extraction electrode and the focuselectrode is either larger or smaller than the distance between thefocus electrode and the lower electrode. The distance between electrodes(and the height of the inter-electrode structures) may be unequal topromote particular lensing patterns (i.e., collimation) and ioncollection in/through the electrode assembly. In some embodiments, theinter-electrode structures may have a perimeter that is aboutcoextensive with the perimeters of the electrodes, as shown in FIG. 2.In other embodiments, the inter-electrode material perimeter may besmaller than the perimeters of the electrodes, for example to facilitateelectrical connections to the electrodes.

FIG. 4 presents a close-up view of a portion of an inter-electrodestructure 450. While FIG. 3 presents a top-down view of aninter-electrode structure, FIG. 4 presents a side view. The portionshown in FIG. 4 may correspond to any part of the inter-electrodestructure, for example a peripheral ring, or an additional support suchas a radial support, chord, rib, etc. The portion may be curved orstraight, as appropriate. The aperture formation or assembly and bondingprocesses may result in significant heating. The heating can causeexpansion of gases and an increase in pressure where the expanded gasesdo not have an easy route for removal. Additionally when the environmentaround the electrode assembly is evacuated or pressurized as would occurduring system start-up or for maintenance, large pressures differencesacross the electrode assembly may occur. For example, gas present in thespace between adjacent electrodes can expand during vacuum pumping ofthe assembly, resulting in increased pressure between the electrodes.Such pressure increases can be dangerous and should be avoided. As such,in various cases the inter-electrode structure 450 may include gaspathways 455 configured to allow gas to escape from the spaces betweenadjacent electrodes. The gas pathways 455 may be provided at anyappropriate dimensions and patterns. The gas pathways 455 should besufficiently large to allow gas to escape without significant pressurebuildup, but should not be so large or closely spaced to compromise thestructural integrity of the inter-electrode structure 450.

In many cases, the inter-electrode structure may be formed/shaped beforeit is attached to the electrodes. In other cases, however, the shape ofthe inter-electrode structure is formed after the inter-electrodestructure is attached to the electrodes. Such shaping may occur bothduring and after formation of the apertures.

FIGS. 5A-5D present cross-sectional views of an electrode assembly 500at different points in time during fabrication. Initially, an extractionelectrode 509, a focus electrode 511 and a lower electrode 513 areprovided without any apertures therein. An inter-electrode layer 520 isprovided between each set of adjacent electrodes. The inter-electrodelayer 520 may be pre-formed (as shown in FIG. 5A), or it may bedeposited directly on the electrodes 509, 511, and/or 513 (e.g., throughphysical vapor deposition, a chemical vapor deposition, sol-geldeposition, spraying, or lamination). The inter-electrode layer 520 mayalso be referred to as an inter-electrode structure or inter-electrodematerial. Next, the inter-electrode layers 520 are connected to theelectrodes to produce electrode assembly 500, as shown in FIG. 5B. Thelayers may be connected by electrostatic bonding in some cases. In othercases, glass frits may be used to bond the layers. In other cases,mechanical structures and/or adhesives are used to secure the layers inplace. Electrostatic and mechanical bonding methods are furtherdiscussed below. After the electrodes 509, 511, and 513 are secured tothe inter-electrode layers 520, apertures 510 are drilled into theelectrode assembly as shown in FIG. 5C. The apertures may be formedthrough laser drilling (e.g., with a CO₂, UV or DPSS laser). mechanicaldrilling (e.g. using a diamond-tipped drill) or other drilling process.Next, the electrode assembly may be exposed to etching chemistry to etchaway at least some of the remaining inter-electrode material betweenapertures in the inter-electrode layers 520. The etching chemistryshould be chosen such that it selectively etches the inter-electrodematerial while leaving the electrode material relatively un-etched. Oneexample chemistry that may be used to etch quartz inter-electrodematerial without etching a silicon-based electrode is hydrofluoric acid.Other etching chemistries that may be used in certain embodimentsinclude BHF, BOE, HCL, NHO₃, Acetic Acid, KOH, H₂N₂, NaOH, NH₄OH, N₂H₄,Acetone or other ketones, Methylene Chloride, Alcohols, TMAH, andcombinations thereof.

In FIG. 5D, the inter-electrode material is not completely etched away.Rather, the inter-electrode material is etched into support shapes 521.The support shapes 521 extend between sets of adjacent electrodes tocontact each electrode in the set. When considered in three dimensions,the support shapes 521 may be separate individual columns (where etchingis more extensive), or the shapes may remain joined to form a supportnetwork (where etching is less extensive). The arrow in FIG. 5Drepresents the trajectory of an ion through an aperture 510 of theelectrode assembly 500.

In order for the electrodes to function as desired, the inter-electrodematerial should not deleteriously interfere with the electric fields/iontrajectories produced by the electrodes. Etching the inter-electrodematerial back from the edges of the apertures helps ensure that theelectrodes function as desired, accelerating and focusing ions withoutarcing or shorting. Etching the inter-electrode material may be done toany desired degree. For example, in some cases the inter-electrodematerial is substantially entirely etched away except in a peripheralregion. In this embodiment, the inter-electrode layer has a ring shapeas shown in panel A of FIG. 3. In other embodiments, a minimal amount ofinter-electrode material is etched away (e.g., the minimum amount neededfor the electrodes to shape ion trajectories as desired).

The degree to which the inter-electrode material is etched depends onthe duration of etching, the strength of the etching solution, and therelative geometry of the apertures that are formed in the electrodes.Longer etching and stronger etching solutions result in a greater degreeof etching and therefore less extensive support shapes. Smallerdistances between nearby apertures similarly results in a greater degreeof etching and less extensive support shapes. There is a tradeoffassociated with the degree to which the inter-electrode material isetched away. On one hand, etching a substantial amount ofinter-electrode material helps ensure that the inter-electrode materialdoes not interfere with the electric fields/ion trajectories produced bythe electrodes. On the other hand, etching a small amount ofinter-electrode material helps maintain the structural support providedby the inter-electrode material. As mentioned above, where theelectrodes are insufficiently rigid, additional inter-electrode materialsupports can help ensure that the electrodes remain flat duringprocessing.

In some implementations, it may be desirable to allow theinter-electrode material to be slightly conductive. This allows theinter-electrode material to bleed off charge in a controlled manner. Forexample glasses used to fabricate the inter-electrode material can bemade slightly conductive by doping with metals such as In, Sn, Pb, Sb,etc.

The embodiment of FIGS. 5A-5D has several advantages. First, theelectrode assembly produced is very strong and rigid due to the presenceof many small inter-electrode material supports between neighboringelectrodes. The electrodes are unlikely to bend or bow, even when verythin electrodes are used over a long time. This ensures that ions passthrough the electrode assembly in a uniform and predictable manner.Another advantage of this embodiment is that material does not becometrapped between electrode layers during formation of the apertures. Inthe embodiment of FIG. 2, for example, electrode material that is laserdrilled (which may be in the form of dust) may become trapped betweenthe extraction electrode 209 and the focus electrode 211, or between thefocus electrode 211 and the lower electrode 213. This dust may need tobe removed before installing the electrode assembly in a reactionchamber. The removal may involve, for example, a wet bath (e.g., in HF,other acids, alcohols, ketones, deionized water, and combinationsthereof), or a gas flushing operation. Where the inter-electrodestructure is instead implemented as a solid layer of inter-electrodematerial, there is no place for the dust to become trapped, except theaperture sidewalls. Further, any dust which sticks to the sidewalls ofthe apertures is removed when the inter-electrode material is etchedback.

As mentioned, the degree of etching is affected not only by the durationof etching and the strength of the etching chemistry, but also by therelative geometries of the apertures in the electrodes. FIGS. 6A-6Cdepict an electrode and electrode assembly according to a particularembodiment. In this example, certain apertures are omitted such that theelectrode assembly 600 formed has a relatively small number of supportshapes 621 after etching. FIG. 6A shows a top-down view of an electrode609 having apertures 610 arranged in a hexagonal pattern. Certainapertures are omitted at positions labeled “s.” The apertures that areomitted may be chosen to provide spatially uniform ion flux over time.The omitted apertures may be evenly distributed across each electrode.In some cases, rotation of the substrate helps average the effect fromsuch omitted apertures.

FIG. 6B presents a cross-sectional view of an electrode assembly 600including an extraction electrode 609, a focus electrode 611, and alower electrode 613, each having an aperture pattern as shown in FIG.6A. Between each pair of adjacent electrodes is an inter-electrodematerial layer 620. FIG. 6B shows the electrode assembly after theapertures 610 are formed, but before the inter-electrode layer 620 isetched back. The electrode assembly 600 of FIGS. 6B and 6C are shownalong the cut 612 shown in FIG. 6A. As shown in FIG. 6B, areas of theelectrode 609 where apertures are regularly present produce relativelynarrow between-aperture structures 630. Conversely, areas of theelectrode 609 where apertures are omitted produce relatively thickerbetween-aperture structures 631. The between-aperture structures 630 and631 each include the extraction electrode 609, the inter-electrode layer620, the focus electrode 611, another inter-electrode layer 620, and thelower electrode 613.

FIG. 6C shows the electrode assembly 600 after the inter-electrode layer620 is etched back. In areas where the apertures 610 were regularlypresent and relatively narrow between-aperture structures 630 wereformed, the inter-electrode layer 620 is completely etched away. Bycontrast, in areas where apertures were omitted and relatively thickerbetween-aperture structures 631 were formed, the inter-electrode layer620 is incompletely removed, and support shapes 621 remain. A supportshape 621 may be formed at each “s” location of FIG. 6A where anaperture was omitted.

Gas pathways similar to those shown in FIG. 4 may be included in theinter-electrode layers of FIGS. 5B-D and FIGS. 6B-C. The gas pathwaysmay be formed through laser drilling or through machining, for exampleusing the same method used to drill the apertures in the electrodeassemblies. The gas pathways may also be formed by pre-machining groovesinto the inter-electrode material prior to assembly. In cases where theinter-electrode material is implemented as a structure (as in FIG. 3,for example), the gas pathways may be formed before the inter-electrodestructure is joined to the electrodes to form the electrode assembly. Itis also possible in such cases to form the gas pathways after assemblyof the electrode assembly, but this may be more difficult. In caseswhere the inter-electrode material is implemented as a solid layer thatis etched simultaneously with the electrodes, the gas pathways may beformed after the electrode assembly is joined together, either before orafter formation of the apertures.

As mentioned above, electrostatic bonding may be used in someembodiments to join the electrodes to the inter-electrode material.Electrostatic bonding is also referred to as anodic bonding and fieldassisted bonding, and is often used to seal glass to silicon or metal.Briefly, electrostatic bonding involves joining a first material to asecond material through application of heat and an electrostatic field.The first material may be the inter-electrode material (e.g., glass),and the second material may be the electrode (e.g., a silicon-basedelectrode). The glass may be provided as a pre-formed layer orstructure, or it may be deposited (e.g., through sputtering, spin-onmethods, or vapor deposition methods) directly on an electrode. Theterms glass and inter-electrode material are used interchangeably inthis section. Those of ordinary skill in the art understand that theterm glass includes many different possible formulations. Theelectrostatic field allows creation of a space charge at the materialinterface, which creates a strong electrostatic attraction between theglass and the silicon. Further, oxygen is driven by the electric fieldfrom the glass to the glass-silicon interface, where it combines withsilicon to form SiO₂, thus creating a strong permanent bond.

In order to perform electrostatic bonding, four basic steps areundertaken: (1) contacting the glass with the silicon-based electrode,(2) heating the glass and electrode, (3) applying an electrostatic fieldto bond the glass to the electrode and thereby form a glass-electrodestack, and (4) cooling down the glass-electrode stack. The bondingprocess is characterized by the bond voltage, and bond temperature. Thebond voltage may be between about 100-10,000 V, for example betweenabout 100-1000 V. The bond temperature may be between about 20-700° C.,for example between about 100-500° C. The electrostatic bonding canoccur at atmospheric pressure, however gas may become trapped at theinterfaces, making voids in the bond. These voids may be prevented byperforming the bonding in a vacuum environment. The vacuum environmentmay be between about 10⁻⁸ Torr and 100 Torr, for example between 10⁻⁵Torr and 10⁻² Torr.

Electrostatic bonding often results in bonds having a strength betweenabout 10-20 MPa when subjected to pull tests. This strength is higherthan the fracture strength of the glass in various cases. In otherwords, once the glass is electrostatically bonded, it may be easier tofracture the glass than to mechanically separate the glass from theelectrode.

One consideration that is relevant when choosing theinter-electrode/glass material is the material's coefficient of thermalexpansion (CTE). It is desirable for the inter-electrode material tohave a CTE that approximates that of the electrodes. Where this is thecase, both types of material will expand and contract in a similarmanner when used in plasma processing. Otherwise, the materials mayexpand and contract non-uniformly, which can introduce tension/stress atthe bond. Such stress can result in a poor quality bond. In some cases,the CTE of the inter-electrode material may differ from the CTE of theelectrode material by no more than about 75%, in some cases by no morethan about 15% in other cases by no more than about 10%. Such matchingof the CTEs helps ensure a high quality bond. Some borosilicate glassescan be formulated to match the thermal expansion coefficient to siliconvery closely. Some examples of CTE matched glasses are Hoya SD-2, fromHoya Corporation, of Tokyo, Japan, or Pyrex® 7740, from Corning Inc., ofCorning, N.Y.

Another factor that affects the choice of inter-electrode material isthe composition of such a material. As mentioned, the inter-electrodematerial may be glass in some cases, and various types of glass may beused. The glass may have a relatively high content of alkali metals(e.g., at least about 1% by weight, for example at least 2% or at least3% by weight), in some cases. Pyrex borosilicate is one example, havinga sodium oxide (Na₂O) content of about 3.5%. The presence of mobilemetals within the glass is advantageous. The positive metal ions (e.g.,Na+) are attracted to the negative electrode, where they areneutralized, by applying a high negative potential to the glass. Thispermits the formation of a space charge at the glass-silicon electrodeinterface, which in turn creates a strong electrostatic attractionbetween the silicon electrode and the glass. Heating the materialsduring bond formation helps increase the mobility of the positive ions.

Optically sensitive types of glass that may be used in certain casesinclude Foturan photosensitive glass (a photo structurable glassceramic) manufactured by Schott Glass Corp. and distributed by Inveniosof Santa Barbara, Calif. These materials can be exposed to light andpreferentially etched away (where exposed). This could be used incombination with laser machining, where the electrodes are lasermachined, while optically sensitive glass (i.e., the inter-electrodestructure) is exposed to light either from a laser or from exposing theelectrode stack to light (using the machined electrode as a shadow maskfor the light). Once exposed, the glass is heated, and then the exposedregions are etched away using one or more of the appropriate glassetchants such as 2-7% dilute HF (by weight). The use of photosensitiveglass eliminates the need for laser drilling which can be difficult formany glasses and fused silica.

In order to fabricate the electrode assembly as shown in FIG. 5B, forexample, four bonds need to be created: (1) one bond between the lowersurface of the extraction electrode 509 and the upper surface of theupper inter-electrode layer 520, (2) one bond between the lower surfaceof the upper inter-electrode layer 520 and the upper surface of thefocus electrode 511, (3) one bond between the lower surface of the focuselectrode and the upper surface of the lower inter-electrode layer 520,and (4) one bond between the lower surface of the lower inter-electrodelayer 520 and the upper surface of the lower electrode 513. In someembodiments, each of these bonds is individually formed. In other cases,two or more of the bonds, for example all of the bonds, are formedsimultaneously.

An example process for forming the electrode assembly is shown in FIG.11. Electrodes 1102 and inter-electrode layer 1103 are cleaned andplaced onto a heated platen 1101 inside vacuum vessel 1104. A heatedpressure plate 1100 is placed on the electrode/inter-electrode materialstack and the air in vacuum vessel 1104 is evacuated. Pressure isapplied to heated pressure plate 1100, and a voltage is applied betweenthe two electrodes 1102, either by making direct contact to theelectrodes 1102 or by applying a voltage between the heated platen 1101and the heated pressure plate 1100. The voltage and temperature areapplied for a given time or until the current density drops to a setvalue. The process can then be repeated to add other electrodes andinter-electrode materials as desired.

In other embodiments, the electrodes may be mechanically securedtogether without electrostatic bonding. Example mechanical joiningmethods are shown in FIGS. 7A-7C. The approaches outlined in thesefigures may also be combined with one another. Mechanical joiningmethods may be particularly advantageous for electrodes made fromrefractory materials. One type of mechanical joining method involvesapplying an adhesive or glass fits between the electrodes to secure theelectrodes together. FIG. 7A illustrates this approach. In this case,electrode assembly 700A includes extraction electrode 709, focuselectrode 711, lower electrode 713, and adhesive layers 730. Exampleadhesives include, but are not limited to, glass frits, epoxies, orother thermo-setting or thermo-plastic polymers, eutectic bondingmaterials, solders, and may include Pb-Based Glass Frits, B-Based GlassFrits, B—P-based glass fits, epoxies, silicones, polyimides, etc.

Another type of mechanical joining method involves cutting one or moreguide holes into each of the electrodes, and inserting a pin or otherstructure through each of the guide holes to align the electrodes. FIG.7B illustrates this approach. Here, electrode assembly 700B includes theelectrodes 709, 711, and 713 mentioned above, as well as pins 736 andelectrode spacers 737. The pins 736 fit in guide holes 735 in each ofthe electrodes. The pins 736 should fit relatively tightly in the guideholes 735 to prevent the electrodes 709, 711 and 713 from moving withrespect to one another. The electrode spacers 737 may be provided tomaintain the proper distance of separation between adjacent electrodes.The electrode spacers 737 may be of any shape (e.g., blocks, rings,etc.), and should be provided in a quantity sufficient to maintain theelectrodes in a flat shape during drilling. The electrode spacers 737may be provided radially interior of the pins 736, as shown in FIG. 7B,or they may be provided outside of the pins 736 if the electrodes aresufficiently rigid. In some cases, the guide holes 735 may be aperturesthrough which ions travel during processing. Notably, only a smallnumber of guide holes 735 need to be drilled before the electrodeassembly 700B is put together and the remaining apertures are formed.The pins 736 may be removed before or after the electrodes are installedin a reaction chamber. Post-installation removal can help ensure thatthe electrodes are installed with the apertures fully aligned. In somedesigns, the pins 736 remain in the electrode assembly 700B, and theentire electrode assembly 700B is installed in, and remains in, thereaction chamber. In such cases, the choice of pin material is moreimportant (the material should be insulating so that different levels ofbias can be applied to each electrode).

A further type of mechanical alignment involves positioning (andsecuring) a first electrode on a precision optical table controlled by alaser interferometer measurement system and optically or mechanicallymeasuring the position of one or more apertures or reference marksetched or machined into the electrode (e.g., such marks being positionedwhere an aperture is desired). Then one inter-electrode material isplaced on top of the first electrode and positioned relative the firstelectrode by measuring the position of one or more apertures orreference marks optically or mechanically with reference to themeasurements of the corresponding marks on the first electrode. Oncealigned to the precision necessary, the inter-electrode material isclamped to the first electrode. Next, a second electrode is positionedrelative to the first electrode in the same manner, and so forth untilthe entire electrode stack is aligned and clamped. After clamping, theassembly may be further bonded using glues. frits or anodic bonding.

A further type of mechanical joining method is shown in FIG. 7C. Theelectrode assembly 700C includes the electrodes 709, 711, and 713 asdescribed above. However, in this example the electrodes are separatedby brackets 740. The bracket 740 may be a mechanical alignment bracketof any suitable shape. Thus, there is no need to drill guide holes inthis case. The brackets may be of any appropriate design. In the exampleof FIG. 7C, the brackets individually support each electrode byextending around the peripheral edge of each electrode. Electrodespacers 737 may be used to help support the electrodes and ensure thatthey remain flat during drilling. Any number of brackets may be used.For instance, a single bracket may be used in some examples. Where thisis the case, the bracket may extend around a substantial portion of theperiphery (e.g., the entire periphery, or at least about 90%, or atleast about 95% of the entire periphery). The bracket may be flexible,or may include a joint that allows the electrodes to be placed into thebracket. In other cases, two or more brackets may be used. The bracketsmay be relatively small (e.g., each bracket supporting the electrodes atone narrow angular spot) or relatively large (e.g., each bracket extendsaround the periphery to some degree to support the electrodes at a widerangular position, up to about 180° per bracket where two brackets areused). Overall, the brackets may wholly or partially support theelectrodes at their periphery. Where multiple brackets are used, thebrackets may fit/snap/otherwise be secured together to provideadditional mechanical stability to the electrode assembly 700C. Thebrackets 740 may be removed before or during installation in thereaction chamber, or they may remain connected to the electrodes duringinstallation and processing. As with the pins 736 of FIG. 7B, thebrackets should be insulating if they are to remain installed duringoperation. Further, if the brackets are present during processing andare shaped to support the entire periphery of the electrodes, thebrackets may include pass-throughs allowing for an electrical connectionto each electrode (for applying the bias to each electrode).

Another type of mechanical joining method involves the use of clamps, asshown in FIG. 7D. Here, the electrodes 709, 711, and 713 are sandwicheddirectly against one another (though additional spacers may be used toseparate the electrodes if desired). A clamp 745 is provided to securethe electrodes against one another. Any number of clamps 745 may beused, with higher numbers of clamps providing additional mechanicalsecurity. Only a single clamp 745 is shown in FIG. 7D for the sake ofclarity.

The embodiments of FIGS. 7B-7C may also be modified such that theelectrodes 709, 711 and 713 are directly in contact with one another,without any spacers between them during aperture formation. It is notnecessary to maintain space between the electrodes while the aperturesare being formed. On the other hand, such space is necessary duringprocessing. As such, where this is the case the electrodes should beseparated and installed individually after the apertures are formed.This embodiment still varies from what is found in the prior art becauseapertures are formed in each of the electrodes simultaneously in asingle unified process and in an extremely aligned manner. In anyimplementation where electrodes are installed individually afteraperture formation, the apertures may be aligned by a laser or throughother optical methods.

Regardless of the method is used to join the electrodes into anelectrode assembly, the apertures may be formed after such assembly isjoined together. The apertures may be formed by laser drilling in somecases. Laser drilling may occur through melting and/or vaporization ofthe workpiece material (i.e., the electrode) through absorption ofenergy from a focused laser beam. In some cases, a high power industriallaser is used, such as a CO₂ laser, UV Laser or DPSS laser.

In certain embodiments, laser drilling at full power results inunacceptable temperature increases, inter-electrode material fracture,or excessive hole taper. To address this issue and allow for cooling,the laser may be pulsed during drilling. The pulsing may reduce thedegree of heating and therefore improve the drilling results. Examplepeak power levels delivered by a laser drill may range between about50-5000 μJ/pulse, for example between about 200-500 μJ/pulse. Where thelaser is pulsed, the frequency of such pulsing may be between about25-500 kHz, for example between about 20-200 kHz. The duration of eachpulse may be between about 1-50 μs, for example between about 5-20 μs.One of ordinary skill in the art would understand that the choice oflaser and the choice of electrode and inter-electrode materials willaffect the optimal power levels, pulsing frequency, pulse duration, dutycycle, etc. As such, the disclosed parameters are provided merely forguidance and are not intended to be exhaustive or limiting.

Laser drilling SiO₂-based inter-electrode materials (e.g., fused silica,or boro-silicate glasses, etc.) has several problems that a bondedelectrode stack can overcome. Firstly, it is common that thelaser-drilled exit hole experiences chipping and breakout on theunderside due to acoustic shock during the drilling process. Since allinter-electrode materials are bonded between electrode materials in thebonded stack, chipping and breakout can be prevented. Secondly,micro-cracking can occur due to heat build-up in thick SiO₂-basedmaterials. Since the inter-electrode material is bonded to thermallyconductive electrodes, heat dissipation pathways are provided tominimize or prevent micro-cracking.

Depending on the configuration of the electrode assembly, the apertureformation process may involve drilling solely through electrodematerial, or through both electrode material and inter-electrodematerial. If the inter-electrode material is shaped and positioned suchthat it does not overlap with the apertures (as shown in FIG. 2), thenthe aperture formation process will only require drilling through theelectrode material. On the other hand, where the inter-electrodematerial overlaps with the desired aperture positions (as shown in FIGS.5B-5D and 6A-6C), the aperture formation process will require drillingthrough both the electrode material and the inter-electrode material.

In some cases, certain parameters are varied during the laser drillingprocess to account for the different materials being etched as thedrilling process takes place. For example, the laser drilling processcan be optimized for each material in the assembly by varying thelaser's power, duty cycle, wavelength, pulse frequency, etc. Thesechanges may be made to accommodate the various laser absorbance,reflectance, oblation temperature, and thermal conductivity propertiesof the different materials in the electrode assembly. Further, asmentioned above, in some cases a different type of process is used todrill through the electrodes vs. to drill through the inter-electrodematerial (e.g., where the inter-electrode material is a light sensitiveglass).

Laser drilled holes in materials often have a taper that is typicallylarger on the laser entrance side and smaller on the laser exit side.This taper is commonly between about 2-10 degrees. Having a hole that issmaller on the plasma source side and larger downstream (i.e., thesubstrate-facing side) maybe advantageous in the electrode stack. Thistaper reduces the amount of ions that scatter off of electrodes andinter-electrode materials as they travel through the electrode stack.Therefore, it may be advantageous that the electrode stack be laserdrilled from the ion exit side of the stack (i.e., the substrate-facingside of the electrode assembly). By laser drilling from this side, thedesired taper can be accomplished.

In certain embodiments the apertures in the electrode stack getprogressively larger, starting from the ion entrance side of the stack.The hole diameter in the electrode stack may increase 0-30% at eachsubsequent electrode (starting from the ion entrance side). For examplethe diameter may increase by 5-15% at each electrode, relative to theelectrode before it. Appropriate aperture patterns and sizes arediscussed above.

In certain embodiments, the apertures are formed by a lithographicprocess followed by an etch process. Since modern lithographic processescan precisely control size and position of the patterns, aperturealignment errors may be reduced significantly. Laser-based, direct-writelithography systems such as the DWL-400, from Heidelberg InstrumentsMikrotechnik GmbH, of Heidelberg, Germany can position the aperturepatterns to within 350 nm or better, and can produce aperture hole sizeprecision of better than 120 nm. This is 500-1000× better than theprecision that can be achieved by mechanical drilling. Other opticallithography systems such as scanners and step-and-repeat systems canproduce similar or better performance. Once lithographic patterns areexposed and developed, these patterns can then be etched into theelectrodes and inter-electrode materials separately. Since the aperturepositional accuracy is very precise, aligning all of the apertures inthe electrode stack, across all electrodes is possible.

Hollow Cathode Emitter

Any of the embodiments herein may be modified to include an additionalelectrode, which may be a hollow cathode emitter electrode. In certainembodiments, the hollow cathode emitter electrode is provided above theextraction electrode to create numerous high density ion sources abovethe extraction electrode. The hollow cathode emitter may be immediatelyabove the extraction electrode in the same manner as the extractionelectrode is immediately above the focus electrode (e.g., with no otherintervening structures besides an optional inter-electrode material asdescribed herein). In effect, each aperture in the hollow cathodeemitter electrode acts as hollow cathode emitter, thereby providingnumerous local high density ion sources. In other embodiments thehollow-cathode emitter may be incorporated within the extractionelectrode itself. The apertures in the hollow cathode emitter electrodeare designed or configured to be aligned with the apertures in the otherelectrodes. The hollow cathode emitter electrode therefore increases theefficiency of active ion generation, as a substantial majority of theions generated in the hollow cathode emitters are successfullytransferred through the electrodes to the wafer. This allows for highdensity ion generation at lower energy levels. Comparatively, where anICP plasma source or other full-wafer (i.e., non-local) plasma source isused, much of the energy used in generating ions may be effectivelywasted because many of the generated ions strike an upper surface of theelectrodes. These ions therefore do not travel through the electrodes,and do not interact with the wafer.

Hollow cathodes typically include a conductive tube/cylinder having anemitter material on the inside surface. In the context of a hollowcathode emitter electrode, the conductive tubes/cylinders are theapertures. The emitter material preferably has a low work function,which allows the material to have a high secondary electron yield.Example emitter materials include, but are not limited to, silicon,tungsten, molybdenum, rhenium, osmium, tantalum, aluminum, titanium, andthoriated tungsten. The emitter may also be coated with a material toenhance secondary electron yield, or prevent corrosion to sputtering.This coating may be vapor deposited, sprayed on, electroplated,electro-less plated, chemical vapor deposited, plasma enhancedchemically vapor deposited, painted on, spun on, etc. Additionally theelectrode material may be anodized. Typically, the electrode containsonly a single material; in other words, the emitter material is theelectrode material. The overall shape (e.g., thickness, diameter) of thehollow cathode emitter electrode may be substantially the same as theshape of the other electrodes. During etching, gas and/or plasma may befed/generated upstream of the hollow cathode emitter electrode. Whereplasma is generated upstream from the hollow cathode emitter electrode,such plasma may be an inductively coupled plasma, a capacitively coupledplasma, a transformer coupled plasma, a microwave plasma, etc. Theplasma may be generated remotely or in the reaction chamber above thehollow cathode emitter electrode. The hollow cathode emitter electrodemay be RF biased, for example between about 50-5,000 W, assuming asingle 300 mm substrate is present. Emitted electrons ionize the gas ineach aperture as the gas travels through hollow cathode emitterelectrode. The ionization mechanism is discussed further below withrespect to FIG. 9.

In certain embodiments, apertures of the hollow cathode emitterelectrode are configured to have a shape that promotes high density ionformation. One example shape that achieves this purpose is afrustoconical aperture. Other shapes such as inverted cones, domes,inverted pyramids, etc. may also be used to promote ion formation.Generally, aperture shapes that are wider on the top compared to thebottom are especially useful.

In certain embodiments, it is desirable to have a gas pressure that ishigher upstream of the hollow cathode emitter than downstream. To enablea pressure drop across the emitter, the gas conductance through theemitter holes should be low. In some cases the gas conductance throughthe electrode stack may be below about 10,000 L/min. For example the gasconductance may be between about 50-1000 L/min. For example, about a 1Torr pressure differential (above vs. below the hollow cathode emitter)can be achieved by narrowing the minimum diameter (dimension d₂ in FIG.8) of the aperture. For example, an array of 1000 apertures, with a d₂diameter of 0.5 mm, and d₃ length 1 mm would have a gas conductance ofabout 800 L/min and would experience about a 1 Torr pressure drop whengas was flowing at about 1 SLM flow rate.

In embodiments where the gas conductance through the electrode assemblyis reduced, a gas by-pass pathway may be used. This gas by-pass pathwaywould be opened to prevent excessive pressure differential across theelectrode assembly, for example during initial pump down of the entireassembly. This gas by-pass then could be closed during operation if apressure differential is desired.

FIG. 8 presents a close-up cross-sectional view of a hollow cathodeemitter electrode 854 having frustoconically shaped apertures 814. Eachaperture 814 has a first diameter d₁ on an upper surface 818 of hollowcathode emitter electrode 854 and a second diameter d₂ on a lowersurface 820 (or wafer side) of hollow cathode emitter electrode 854. Thefirst diameter d₁ is larger than the second diameter d₂. In some cases,the first diameter d₁ is between about 1 mm-20 cm. The second diameterd₂ may be between about 0.1 mm-10 cm. The ratio of the first diameter tothe second diameter (d₁/d₂) may be between about 1.2-10. As can be seen,the upper side of the apertures 814 are generally frustoconical inshape, being tapered inward by a 90° chamfer until the interior diameterthereof is equal to d₂. The chamfer angle is measured as shown in FIG.8. In other embodiments the conical section has a different chamferangle, for example between about 45-120°. The frustoconical sectionmeets the cylindrical section roughly halfway through the thickness ofthe hollow cathode emitter electrode 854, and thus apertures 814 may becharacterized as having both a frustoconical section 817 and acylindrical section 819. The cylindrical section 819 of aperture 814 hasa height represented by d₃ in FIG. 8. In some cases, the height of thecylindrical section 819 is between about 0.2 mm-2 cm. In these or othercases, the height of the frustoconical section 817 is between about 0.5mm-2 cm. The aperture diameters and heights herein, while shown in thecontext of an aperture having a frustoconical section and a cylindricalsection, may also apply to apertures of different but similar shapes.

FIG. 9 illustrates the micro-jet, low-energy ion generation regionthrough the chamfered apertures 914 of the hollow cathode emitterelectrode 954. As a result of the primary plasma discharge above thehollow cathode emitter electrode 954, a local sheath 922 is created inthe apertures 914, thereby resulting in an electric field. The primaryplasma discharge may be from any appropriate plasma source upstream ofthe hollow cathode emitter electrode 954. Example plasma sources includeinductively coupled plasma sources, capacitively coupled plasma sources,microwave plasma sources, remote plasma sources, etc.

The electrons and ions from the primary discharge enter the apertures914 and create a current path (indicated by dashed arrows 923) througheach aperture and to the lower surface 920 of the hollow cathode emitterelectrode 954. As the current lines (arrows 923) converge approachingthe apertures 914, the current density increases, causing the formationof a denser plasma in the aperture, thereby forming the plasma jet whichhas a narrow plasma sheath. The increased plasma density of the microjetmay also increase the neutral temperature which reduces the density ofneutrals in the apertures. The combination of these effects may increasethe electron temperature and change the chemistry of the discharge inthe micro-jet. In addition, the ions are also accelerated by the sheathand strike the inner surface 924 of the apertures 914, thereby ejectingsecondary electrons. The narrower sheaths associated with high plasmadensity plasma permit the acceleration of the electrons across thesheath 922 with few collisions resulting in the creation of veryenergetic electrons in the micro-jet. The secondary electrons gainenough energy so as to collide with neutral gas molecules, therebyionizing them and creating a micro jet shaped discharge 926 through theapertures.

In some cases, the primary plasma discharge may be omitted. In otherwords, the hollow cathode emitter electrode may be the sole source ofplasma/ions. In these embodiments, the initial high energy electronsthat begin the cascade for ion formation are generated as a result of anRF bias applied to the hollow cathode emitter electrode. High voltagegradients and/or long apertures help promote formation of themicro-jets. These considerations are less important where high energyelectrons are also being provided from a primary plasma upstream of thehollow cathode emitter electrode. Where no separate plasma source isincluded beyond the hollow cathode emitter electrode, the RF bias on thehollow cathode emitter electrode may be between about 500-10,000 W.Where a separate plasma source is included, the bias may be lessextensive.

The micro-jet discharge 926 is the primary source of ions thatultimately impinge on the wafer. In addition, it has also beenempirically determined that a low aspect ratio (diameter d₂ divided byheight d₃) of the apertures 914 enhances the micro jet discharge.However, if the height of the apertures 914 (i.e., thickness of thehollow cathode emitter electrode 954) is made too small, the capacityfor cooling of the electrode is eliminated. On the other hand, if thediameter of an aperture is made too large so as to lower the aspectratio, the effectiveness of the hollow cathode emitter electrode inuniformly dispersing the plasma discharge is diminished. Accordingly,the apertures 914 of the present embodiments may be configured so as toprovide a lower aspect ratio for effective generation and transport ofan ion rich plasma, through the apertures to the wafer, while stillallowing effective electrode cooling.

The sizing and aspect ratio of the apertures 914 needed to generatereliable micro jets therein is a function of the process conditions,including parameters such as plasma power, pressure, gas composition,etc. In this process, the “lighting” of micro jets in the apertures 914is required to achieve uniform processing. The process describedachieves the uniform and reliable lighting of the micro jets to producesuch uniform processing. This differs from other applications, such asgrids, in which a perforated plate used for shielding orgenerating/modulating electric or electro-magnetic fields has holes thatdo not reliably form micro jet discharges. Similarly, the presentinvention embodiments differ from other prior art where a perforatedplate with holes is used as an electron or ion lens in which the plasmapasses through the apertures in the plate without the formation of amicro jet discharge.

The use of a hollow cathode emitter electrode allows for high densityion extraction using relatively lower voltages/extraction fields. Thismay help reduce on-wafer damage from high energy ions. Where a hollowcathode emitter is used, it may be RF biased between about 100-10,000 W.In such cases, the extraction electrode may be biased between about20-10,000 V with respect to the lower electrode, the focus electrode maybe biased at an intermediate potential between the extraction electrodeand the lower electrode, or a potential higher than the extractionelectrode. The lower electrode may be grounded or biased relative to thelevel of the wafer, for example between about 0-negative 1,000 Vrelative to the substrate. A potential gradient between theextraction/focus/lower electrodes as installed may be between about0-5,000 V/cm.

Reflector

Any of the embodiments herein may be modified to include a set ofreflectors below the lower electrode. The reflectors may be used toneutralize the ion beam without the use of a costly flood gun. Inparticular, ions that impact the reflector surface pick up electrons tobecome neutral particles. Further, the reflectors may capture sputteredmaterial, which may travel at relatively low kinetic energy and stick tothe reflectors. In some cases, the reflectors are made from a materialsuch as degeneratively doped silicon, metal foil or metal plate (e.g.,silicon, tungsten, molybdenum, rhenium, osmium, tantalum, aluminum,titanium, or thoriated tungsten).

FIG. 10 illustrates a reaction chamber 1000 for performing ion beametching. In this example, four electrodes are used including a hollowcathode emitter electrode 1054, an extraction electrode 1009, a focuselectrode 1011, and a lower electrode 1013. As shown in FIG. 10, theapertures 1010 in the hollow cathode emitter electrode 1054 may have afrustoconical or other shape as described above. Below the lowerelectrode 1013, a set of reflectors 1020 are attached. The reflectors1020 may have an angle α with respect to the surface normal of electrode1013 between about 0.5-20°. The length of the reflectors 1025 may besufficiently long to close off the apertures from a line-of-sightprojection through the aperture holes onto the substrate. Therefore, thelength 1025 may be greater than or equal to the diameter of theapertures in electrode 1013 divided by the sine of α. The spacingbetween adjacent reflectors may be the same as the spacing betweenadjacent apertures. The reflectors are positioned parallel to oneanother such that they uniformly alter the ion trajectories. Because thereflectors 1020 change the trajectory of the ions/particles as theyenter the substrate processing region 1015, the particles leaving thereflector 1020 do not travel straight downward. If it is desired thatthe particles impact the wafer 1001 at a normal angle (i.e., 90°), thewafer 1001 may be tilted to accommodate the angled trajectory of theparticles. Tilting may be done by controlling the substrate supportpedestal 1003. In some cases, the wafer may be tilted and untilted tovarious degrees during etching to direct the ions/particles as needed.In other cases the electrode assembly may be tilted with respect to thesubstrate. Tilting may help achieve good etching results at featuresidewalls, for example. Such tilting may occur regardless of whether areflector 1020 is used.

The other features of FIG. 10 are similar to those shown in FIG. 1. Forexample, plasma is generated through the ICP plasma source 1007. Theplasma is generated in a primary plasma generation region 1005.

The reflectors may be pre-formed and attached to an electrode assemblyin some cases. The reflector formation process may involve shapingsilicon or metal pieces into desired shapes. Alternatively or inaddition, the reflector formation process may involve creation ofapertures in a plate of material. Apertures may be formed through lasercutting or through the electrolytic bath/metal ball process describedbelow.

In a particular embodiment, the reflectors may be formed at the sametime or immediately following formation of the apertures in an electrodeassembly. Metal balls (e.g., molybdenum or gold balls) may be used toform the apertures in some cases. A reflector precursor layer may beprovided below the lower electrode. In some cases the reflectorprecursor layer is silicon (e.g., degeneratively doped silicon), whichmay be electrostatically bonded to the lower electrode. The reflectorprecursor layer may be a solid layer of material, without any aperturesor other pathways. Once the entire electrode assembly is assembled withthe reflector precursor layer attached, the assembly may be placed intoan electrolytic bath. The electrodes may already have apertures drilledtherein, or the electrode apertures may be formed in the electrolyticbath. The bath solution may include KOH, KOH+IPA, ethylenediamine,ethylenediamine+pyrocatechol, hydrazine, hydrofluoric acid, H₂O₂, orcombinations thereof, for example. Metal balls may be placed on theassembly where the apertures are desired. In some cases the uppermostelectrode (e.g., a hollow cathode emitter or an extraction electrode)includes pre-drilled divots or holes designed to hold/secure the metalballs in place where the apertures are desired. In one embodiment, themetal balls are chosen to have a catalytic reaction to the silicon. Forexample, silicon is etched in a solution of HF+H₂O₂+H₂O in the presenceof silver. Placing silver balls on the surface while immersing theelectrode stack in the etchant solution will only etch the silicon wherethe balls contact the silicon surface. Other known metal catalystsinclude gold and platinum. An electric field may then be applied tocause the metal balls to cut through the electrode assembly. Theapertures may be formed individually (e.g., using one metal ball at atime), in groups/waves, or all at once.

Gravity may play a role in this process, with the metal balls cuttingthrough the electrode assembly material in a direction directly towardthe center of the Earth. When the metal balls reach the interfacebetween the lower electrode and the reflector precursor layer, theentire electrode assembly may be tilted. Tilting may also occur slightlybefore or after this interface is reached (e.g., when the balls areabout halfway or more through the material). The metal balls continue tofall in a downward direction, cutting very straight apertures into thereflector precursor layer. The apertures in the reflector precursorlayer are aligned with the apertures in the electrodes. However, thereis not a direct line of sight through the electrodes and reflector layerdue to the angle created at (or near) the interface between the lowerelectrode and the reflector layer.

The metal balls used to create the apertures may have a diameter betweenabout 1 mm-5 cm. In some cases, a multi-step process is used to createthe apertures. The first step may involve creating small apertures withmetal balls as discussed above (with or without a reflector being formedsimultaneously). A second step may involve enlarging the aperturescreated in the first step, for example by laser drilling, diamond bitdrilling, or other machining methods. The second step may be performedfrom either side of the electrode assembly (e.g., from the top and/orbottom). Care should be taken to ensure that the second step does notoverly remove material at the interface between the lower electrode andthe reflector layer (if present).

As mentioned, the metal ball aperture formation processes may also beused where the electrode assembly does not include any reflector.Further, the metal ball aperture formation process may be used to formapertures in a reflector that is not yet attached to an electrodeassembly.

Chamber Liner

One issue that arises in certain etching operations is the deposition ofundesirable particles on a substrate during etching. The particles maybe sputtered off of internal reaction chamber surfaces, for example dueto exposure to plasma. The particles then fall onto the surface of thesubstrate where they can cause defects.

In order to address this problem, any of the embodiments describedherein may be modified to include a sputter-resistant chamber liner. Thechamber liner helps minimize sputtering and therefore deposition ofunwanted particles on a substrate during etching. The chamber liner maybe removable in certain cases.

The material used for the chamber liner should be resistant tosputtering under the typical reaction conditions used in the reactionchamber. The chamber liner may have a sputtering yield of ≦0.2 for theion and ion energy used. Example materials include carbon, silicon,titanium, molybdenum, tungsten, and tantalum.

The liner may be configured to be easily removed for cleaning orreplacement.

The liner may cover the chamber walls and floor. In some cases, theliner is designed to leave certain surfaces exposed. These non-exposedsurfaces may include the substrate, the electrodes, viewports, detectorwindows, in-situ detectors, charge neutralization heads, and the like.The liner may be designed to follow the contour of the various internalreaction chamber surfaces. In certain cases, a chamber liner may have athickness between about 1 mm-3 cm, for example between about 2 mm-2 cm.

Substrate Rotation During Etching

In various embodiments, it may be beneficial to rotate and/or tilt thewafer during etching. Wafer rotation can help average the etchingresults over the face of the substrate, thereby promoting within-waferuniformity. Wafer rotation may be achieved by rotating the support onwhich the substrate is positioned. This support is sometimes referred toas a pedestal, chuck, electrostatic chuck, substrate fixture, etc.Tilting the wafer during etching can be beneficial in controlling theetching profile, especially at the sidewalls of etched features. Tiltingis similarly accomplished by tilting the substrate support. In somecases, tilting is done such that the ions/particles impact the substrateat an angle that is about 25° or less (e.g., about 5° or less) from anormal angle. In other cases, tilting may be 45° or less. In othercases, tilting may be more extensive, for example about 85° or less froma substrate normal angle.

The substrate support typically contains various electrical and fluidicconnections. These connections may provide power, cooling fluids, etc.to the substrate support. The power and cooling fluids may originatefrom a position within the reaction chamber (such position being removedfrom the substrate support), or from a position outside of the reactionchamber. The electrical and fluidic connections render substraterotation and tilting more difficult. For instance, a wire connected tothe substrate support may wrap around the substrate support (e.g.,around or within a stem of the support in some cases) as the substraterotates during an etching process. This wraparound can quickly preventfurther rotation of the substrate. Specialized seals may be provided incertain cases to allow the connections to rotate along with thesubstrate support. These seals accommodate the connections and preventthem from becoming tangled around the substrate support. However, theseseals (sometimes referred to as rotating vacuum seals) are susceptibleto leakage, making it difficult to maintain a desired low pressurewithin the reaction chamber. The seals require regular maintenance toaddress the leakage issues. As such, there is a need for an improvedmethod of rotating the substrate during etching that accommodates theelectrical and fluidic connections to the substrate support.

In certain implementations, substrate rotation may be accomplished in amulti-step cyclic process. A first step of the process involves rotatingthe substrate in a first direction (e.g., clockwise), and a second stepinvolves rotating the substrate in a second direction (e.g.,counterclockwise), opposite the first direction. By repeating these twosteps and regularly rotating the substrate in each direction, theelectrical and fluidic connections can be wound and unwound around thesubstrate support to a manageable degree. An appropriate and reasonableamount of slack may be provided in each connection made to the substratesupport. For instance, electrical and fluidic connections may beprovided with sufficient slack to permit the substrate to rotate aparticular amount in either direction.

As used herein, the rotation configuration of a substrate support ismeasured from a central measuring point and is represented by bothpositive and negative values, depending on the direction of rotation(clockwise rotation being positive). A substrate support that isconfigured to rotating ±n degrees from the central measuring point isone that rotates 2n degrees in either direction overall. The factor of 2is introduced due to the fact that the rotation is measured from thecentral measuring point, and the fact that the substrate can be rotatedin either direction from this measuring point. For instance, a substratesupport capable of rotating ±180° can actually rotate a full turn (360°)in either direction when considering the full range of motion (i.e.,from one rotational extreme to the other). The following rotationpattern is given to further clarify how the rotation capability ismeasured and described herein. In this example, a substrate starts at astarting position and rotates +180° clockwise, then −360 degreescounterclockwise, then +360° clockwise, then −360° counterclockwise,etc. In each 360° rotation, the first 180° effectively undoes theprevious rotation, and the second 180° continues rotating the substratein the new direction. In this example, the starting position of thesubstrate corresponds to a rotation of 0°. Of course, the substrate mayalso start a process from other positions. In one example, the substratestarts at a starting position corresponding to a rotation of −180°, thenrotates +360° clockwise, −360° counterclockwise, +360° clockwise, etc.In this example, only full turns are used. Both this and the previousexample correspond to substrate supports that are configured to rotate±180°.

In certain embodiments, the substrate support is designed or configuredto rotate between about ±180° and ±215°, In another case, the substratesupport may be designed or configured to rotate between about ±180°. Theangular extent of rotation may be chosen to allow multi-directional ionbombardment without harming the electrical and fluidic lines connectedto the substrate support. The angular extent of the rotation may bechosen based on the length and flexibility of the electrical and fluidicconnections used. Longer and more flexible connections permit moreextensive rotations. Where more extensive rotations are used, the extraconnection length may be managed as described below.

While these angular ranges are disclosed with respect to a substratesupport designed or configured to rotate as stated, those of ordinaryskill in the art understand that various other components (e.g., theelectrical and fluidic connections, a motor used to rotate the substratesupport, etc.) are part of the configuration of the substrate support.In other words, the substrate support, electrical and fluidicconnections to the substrate support, and any related structures maytogether be designed or configured to permit the rotations disclosedabove. A controller may be used to control the rotation of the substratesupport and substrate. The controller may have instructions to rotatethe substrate according to any of the angular ranges or patternsdisclosed herein.

In order to control the rotation angle, an indexing system may be used.Such a system may designate/define different angular locations on thesubstrate (e.g., 0°, 1°, . . . 359°), and track the rotation of thesubstrate according to these locations. The rotation may be trackedthrough optical means in some cases. For instance, a substrate holdermay have a plurality of marks (e.g., 360 marks, each separated by 1°,though any suitable number of marks may be used) that can be tracked byan optical system as the substrate rotates. An optical encoder may beused in some cases. In other cases, a stepper motor is used to rotatethe substrate. The stepper motor may rotate the substrate as describedherein, carefully controlling the angular rotation of the substrate overtime. A stepper motor may divide a full rotation into a number of equalsteps (e.g., 360 steps, each separated by 1° or less, though anyappropriate number of steps may be used). The motor's position, andtherefore the angular position of the substrate holder and substrate,can be controlled to move between designated steps without the need forany feedback sensors. Other rotational indexing systems may also beused, so long as they allow the angular/rotational position to beaccurately tracked at the relevant rotation speeds. Angular positiontracking may be particularly beneficial for applications such as MRAM,and STT-RAM. For example, in MRAM and STT-RAM cases, there is an axisdependence in the magnetic moment. Such dependence makes angular controlquite beneficial. In some cases such as 3D devices it may be beneficialto rotate the substrate in 180° steps, or in some cases 90° steps, or inother cases 45° steps, and in other cases 30° steps.

The electrical and fluidic lines may connect with the substrate supportat various locations. Where the lines contact closer to the center ofthe substrate support, less slack is needed in the lines to accommodaterotation of the support. In some cases the electrical and fluidic linespass upwards within or substantially within a central stem of thesubstrate support. This configuration may be beneficial in minimizingany effects related to having wires and other connections moving aroundthe processing chamber during etching. Instead, movement of theelectrical and fluidic connection lines is limited to the internalregion of the stem of the substrate support. The connection lines shouldbe sufficiently flexible to accommodate the movements.

In certain cases, a simple back-and-forth rotation of the substrateduring etching results in a poor etching profile for etched features.The poor profile may result from ion directionality and the fact thatthe features are impacted somewhat unevenly as the substrate rotatesback and forth. This problem is especially relevant when theions/particles are directed at the substrate at a non-normal angle. Forexample, where non-normal incident ion beams are used in the context ofa repeating +360°, −360° rotation pattern, a first side of a feature maybe etched from the direction of the ion beam during two subsequentpartial rotations (i.e., a portion of the clockwise rotation immediatelybefore switching rotation direction and a portion of thecounterclockwise rotation immediately after switching rotationdirection) before the opposite side of the feature is exposed to thenon-normal ion beam. This “double exposure” on the first side of thefeature may not be precisely balanced out by the “double exposure” onthe opposite side of the wafer that happens in subsequent rotations. Themismatch may occur for a variety of reasons including, for example, thechanging feature shape (e.g., due to etching as well as redeposition ofetching byproducts). The resulting etch profiles for vertical shapes maybe bowed or “C” shaped in some cases.

In order to address these etching profile problems, the rate of rotationmay be varied during etching. In one example, the substrate rotatesslowly in one direction (e.g., clockwise) and quickly in the oppositedirection (e.g., counterclockwise). An example rotation pattern may be:+360° (slow clockwise), −360° (fast counterclockwise), +360° (slowclockwise), −360° (fast counterclockwise), etc. In another example, thesubstrate rotates slowly during an initial portion of a rotation in onedirection, and quickly during a final portion of the rotation in thatdirection (or vice versa). For instance, the substrate may rotateaccording to the following rotation pattern: +180° (slow clockwise),−180° (fast counterclockwise), −180° (slow counterclockwise), +180°(fast clockwise), etc. (repeating from the first step). Examples of slowrotation rates may be between about 1-10 RPM. Examples of fast rotationrates may be between about 10-500 RPM. The fast rotation rate may befaster than the slow rotation rate by a factor of at least about 5.

In other embodiments, the system may be designed or configured tominimize or stop the ion/particle flux during certain portions of theetching process, for example during periods where the substrate isrotating in a particular direction, or during certain portions (e.g.,first half or second half) of each individual rotation. One examplerotation pattern may be: +180° clockwise (with ion/particle fluximpacting the wafer), −180° counterclockwise (with no ion/particle fluximpacting the wafer), −180° counterclockwise (with ion/particle fluximpacting the wafer), +180° clockwise (with no ion/particle fluximpacting the wafer, etc. (repeating from the first step). A shutter maybe used to control the flux delivered to the wafer. Alternatively or inaddition, the plasma may be ignited and extinguished as needed toprovide ions/particle flux to the wafer when desired. Alternatively thevoltage to one or more of the electrodes may be rapidly switched to adifferent voltage that block the ions from reaching the substrate.

System Controller

In some implementations, a controller is part of a system, which may bepart of the above-described examples. Such systems can comprisesemiconductor processing equipment, including a processing tool ortools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller, depending on the processingrequirements and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the controller may be defined as electronics havingvarious integrated circuits, logic, memory, and/or software that receiveinstructions, issue instructions, control operation, enable cleaningoperations, enable endpoint measurements, and the like. The integratedcircuits may include chips in the form of firmware that store programinstructions, digital signal processors (DSPs), chips defined asapplication specific integrated circuits (ASICs), and/or one or moremicroprocessors, or microcontrollers that execute program instructions(e.g., software). Program instructions may be instructions communicatedto the controller in the form of various individual settings (or programfiles), defining operational parameters for carrying out a particularprocess on or for a semiconductor wafer or to a system. The operationalparameters may, in some embodiments, be part of a recipe defined byprocess engineers to accomplish one or more processing steps during thefabrication of one or more layers, materials, metals, oxides, silicon,silicon dioxide, surfaces, circuits, and/or dies of a wafer.

The controller, in some implementations, may be a part of or coupled toa computer that is integrated with, coupled to the system, otherwisenetworked to the system, or a combination thereof. For example, thecontroller may be in the “cloud” or all or a part of a fab host computersystem, which can allow for remote access of the wafer processing. Thecomputer may enable remote access to the system to monitor currentprogress of fabrication operations, examine a history of pastfabrication operations, examine trends or performance metrics from aplurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller receives instructionsin the form of data, which specify parameters for each of the processingsteps to be performed during one or more operations. It should beunderstood that the parameters may be specific to the type of process tobe performed and the type of tool that the controller is configured tointerface with or control. Thus as described above, the controller maybe distributed, such as by comprising one or more discrete controllersthat are networked together and working towards a common purpose, suchas the processes and controls described herein. An example of adistributed controller for such purposes would be one or more integratedcircuits on a chamber in communication with one or more integratedcircuits located remotely (such as at the platform level or as part of aremote computer) that combine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, anatomic layer deposition (ALD) chamber or module, an atomic layer etch(ALE) chamber or module, an ion implantation chamber or module, a trackchamber or module, and any other semiconductor processing systems thatmay be associated or used in the fabrication and/or manufacturing ofsemiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

The apparatus used for performing the disclosed embodiments oftenincludes a system controller having programming to control the etchingprocess. The controller may execute system control software, which maybe stored in a mass storage device, loaded into a memory device, andexecuted on a processor. The software may be transferred over a networkin some cases. Various process tool component subroutines or controlobjects may be written to control operation of the process toolcomponents necessary to carry out various process tool processes. Thesystem control software may be coded in any suitable computer readableprogramming language. In some embodiments, the system control softwaremay include input/output control (IOC) sequencing instructions forcontrolling the various parameters discussed herein. The systemcontroller may also be associated with other computer software and/orprograms, which may be stored on a mass storage device or memory deviceassociated with the controller. Examples of programs or sections ofprograms for this purpose include a substrate positioning program, aplasma gas control program, a reactant gas control program, a pressurecontrol program, a temperature control program, and a plasma controlprogram.

A substrate positioning program may include code for process toolcomponents that are used to load and unload the substrate onto thesubstrate support. A plasma gas control program may include code forcontrolling the composition and flow rates of gas(es) used to generatethe plasma from which ions are extracted. A reactant gas control programmay include code for controlling the composition, flow rate, andpressure at which other reactant gases are delivered. A pressure controlprogram may include code for controlling the pressure at whichindividual reactants are delivered, the pressure at which reactants areremoved, and the pressure at which the substrate processing region ismaintained. A temperature control program may include code forcontrolling heating and/or cooling equipment used to maintain thesubstrate, substrate support, and/or substrate processing region at aparticular temperature. A plasma control program may include code forgenerating the plasma at certain powers and frequencies.

The system control software may include instructions for deliveringreactants at the flow rates and/or pressures disclosed herein. Suchinstructions may relate to delivery of a gas used to generate plasma(from which ions are extracted), or they may relate to delivery of oneor more gases provided separately (i.e., not used to generate plasma).

The system control software may further include instructions formaintaining the substrate processing region at a certain pressure. Thesystem control software also typically includes instructions forcontrolling the timing of the etching process. In many cases thecontroller also controls the bias applied to each of the electrodes. Assuch, the system control software may include instructions for applyinga first bias to the extraction electrode, a second bias to the focuselectrode, a third bias (or ground conditions) to the lower electrodeand substrate/substrate support, and a fourth bias to the hollow cathodeemitter electrode. In some embodiments, the instructions further includemaintaining the substrate and/or substrate processing region at aparticular temperature through heating or cooling.

Where a shutter is used to modulate ion flux, the system controlsoftware may include instructions to modulate the ions by opening andclosing the shutter at desired times (e.g., during particular portionsof the rotation pattern as described above). In a particular embodiment,the software includes instructions to open the shutters (therebyallowing ions to impinge on the wafer surface) only when the substrateis rotating in a particular direction or at a particular speed.

With respect to plasma generation, the system control software mayinclude instructions for providing a plasma generation gas at aparticular flow rate, temperature, and/or pressure. The instructions mayfurther relate to the amount of power (e.g., RF power) used to generatethe plasma, and the frequency at which such power is delivered.

In some embodiments, a user interface may be associated with a systemcontroller, the user interface may include a display screen, graphicalsoftware displays of the apparatus and/or process conditions, and userinput devices such as pointing devices, keyboards, touch screens,microphones, etc.

In many embodiments, the system controller is used to adjust otherprocess parameters. Such parameters may include, but are not limited to,reactant gas compositions, flow rates, and pressures, plasma generationgas composition, flow rates, and pressures, pressure in the substrateprocessing region, bias applied to the individual electrodes,temperature, plasma conditions (e.g., frequency and power), position ofthe wafer, etc.

Signals for monitoring the process may be provided by analog and/ordigital input connections of the system controller from various processtool sensors. The signals for controlling the process may be output onthe analog and digital output connections of the controller.Non-limiting examples of process tool sensors that may be monitoredinclude mass flow controllers, pressure sensors, thermocouples, etc.Appropriately programmed feedback and control algorithms may be usedwith data from these sensors to maintain process conditions.

The various hardware and method embodiments described above may be usedin conjunction with lithographic patterning tools or processes, forexample, for the fabrication or manufacture of semiconductor devices,displays, LEDs, photovoltaic panels and the like. Typically, though notnecessarily, such tools/processes will be used or conducted together ina common fabrication facility.

Lithographic patterning of a film typically comprises some or all of thefollowing steps, each step enabled with a number of possible tools: (1)application of photoresist on a workpiece, e.g., a substrate having asilicon nitride film formed thereon, using a spin-on or spray-on tool;(2) curing of photoresist using a hot plate or furnace or other suitablecuring tool; (3) exposing the photoresist to visible or UV or x-raylight with a tool such as a wafer stepper; (4) developing the resist soas to selectively remove resist and thereby pattern it using a tool suchas a wet bench or a spray developer; (5) transferring the resist patterninto an underlying film or workpiece by using a dry or plasma-assistedetching tool; and (6) removing the resist using a tool such as an RF ormicrowave plasma resist stripper. In some embodiments, an ashable hardmask layer (such as an amorphous carbon layer) and another suitable hardmask (such as an antireflective layer) may be deposited prior toapplying the photoresist.

It is to be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. As such, various acts illustrated may beperformed in the sequence illustrated, in other sequences, in parallel,or in some cases omitted. Likewise, the order of the above describedprocesses may be changed.

The subject matter of the present disclosure includes all novel andnonobvious combinations and sub-combinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

What is claimed is:
 1. A method of making an electrode assembly for usein an ion beam etching reactor, the method comprising: providing a firstelectrode, a second electrode and a third electrode; providing andsecuring a first inter-electrode structure such that it is immobilizedbetween the first electrode and the second electrode, and providing andsecuring a second inter-electrode structure such that it is immobilizedbetween the second electrode and the third electrode, wherein the firstelectrode, second electrode, third electrode, first inter-electrodestructure, and second inter-electrode structure are substantiallyvertically aligned with one another to form the electrode assembly; andforming a plurality of apertures in the first electrode, secondelectrode and third electrode while the first inter-electrode structureand the second inter-electrode structure are immobilized in theelectrode assembly.
 2. The method of claim 1, wherein one or more of theelectrodes comprise degeneratively doped silicon, wherein securing thefirst inter-electrode structure comprises attaching the firstinter-electrode structure to the first electrode and/or to the secondelectrode, and wherein securing the second inter-electrode structurecomprises attaching the second inter-electrode structure to the secondelectrode and/or to the third electrode.
 3. The method of claim 2,wherein securing one or more of the inter-electrode structures compriseselectrostatically bonding one or more of the inter-electrode structuresto at least one of the electrodes.
 4. The method of claim 1, whereinsecuring one or more of the inter-electrode structures comprisesproviding an adhesive or glass frit to secure the one or moreinter-electrode structures to one or more of the electrodes.
 5. Themethod of claim 1, wherein securing the first inter-electrode structureand securing the second inter-electrode structure comprise providingbrackets or clamps that directly or indirectly secure the firstinter-electrode structure and the second inter-electrode structure andthat directly secure at least the first electrode and the thirdelectrode.
 6. The method of claim 1, wherein forming apertures in firstelectrode, second electrode and third electrode further comprisesforming apertures in the first inter-electrode material and in thesecond inter-electrode material, and further comprising after formingthe apertures, immersing the electrode assembly in etching solution tothereby etch and remove at least a portion of the first inter-electrodelayer and a portion of the second inter-electrode layer.
 7. The methodof claim 6, wherein immersing the electrode assembly in etching solutionresults in the formation of support structures in contact with eitherthe first electrode and the second electrode, or in contact with thesecond electrode and the third electrode, and wherein the supportstructures are formed from the first inter-electrode structure and thesecond inter-electrode structure.
 8. The method of claim 1, wherein thefirst, second and third electrodes and the first and secondinter-electrode structures have coefficients of thermal expansion (CTE)that differ from one another by about 50% or less.
 9. The method ofclaim 1, wherein forming the apertures comprises drilling the apertureswith a laser.
 10. The method of claim 1, wherein the apertures in thethird electrode have a diameter that is between about 0-30% larger thana diameter of the apertures in the second electrode, and wherein thediameter of the apertures in the second electrode is between about 0-30%larger than a diameter of the apertures in the first electrode.
 11. Themethod of claim 1, wherein one or more of the electrodes have apertureswhich are tapered at an angle of about 10° or less.
 12. The method ofclaim 1, further comprising attaching a reflector to the thirdelectrode, wherein the reflector blocks a direct line-of-sight throughthe electrode assembly.
 13. The method of claim 1, further comprisingforming gas pathways in the first inter-electrode structure and/or inthe second inter-electrode structure, wherein the gas pathways allow gasto escape outwards from an interior region of the electrode assembly.14. The method of claim 1, further comprising before or after formingthe apertures, providing a fourth electrode to the electrode assembly,the fourth electrode being provided above the first electrode, whereinthe fourth electrode forms a hollow cathode emitter electrode comprisinga plurality of hollow cathode emitters.
 15. The method of claim 14,wherein the hollow cathode emitter electrode comprises an upper surfaceand a lower surface, the lower surface facing the first electrode, andfurther comprising, before, during, or after forming the apertures inthe first, second, and third electrodes, forming a plurality of holes inthe hollow cathode emitter electrode, each hole having a diameter thatis larger at the upper surface and smaller toward the lower surface,wherein the holes are aligned with a position of the apertures after theapertures are formed in the first, second, and third electrodes.
 16. Themethod of claim 14, wherein the holes in the hollow cathode emitterelectrode comprise a lower cylindrical portion and an upper variablediameter portion.
 17. The method of claim 16, wherein the upper variablediameter portion comprises a funnel shape.
 18. A method of etching asemiconductor substrate, the method comprising: positioning a substrateon a substrate support, wherein a rotation mechanism coupled to thesubstrate support is configured to rotate the substrate at an accuracyof about 2° or better; applying a first bias to a first electrode and asecond bias to a second electrode, wherein the first and secondelectrodes comprise apertures therein, and supplying plasma above thefirst and second electrodes, wherein ions pass through the apertures inthe first and second electrodes toward a surface of the substrate; whilesupplying the plasma, cyclically rotating the substrate and substratesupport in a first direction and in a second direction that is oppositethe first direction; and etching the substrate as a result of ions orparticles impacting the surface of the substrate while the substrate isrotated.
 19. The method of claim 18, wherein the substrate holder isconfigured to rotate about ±215° or less.
 20. An apparatus for etching asemiconductor substrate, the apparatus comprising: a reaction chamber; asubstrate support; an inlet for supplying one or more gases or plasma tothe reaction chamber; a first electrode, a second electrode, and a thirdelectrode, each having a plurality of apertures therein, wherein thesecond electrode is positioned below the first electrode, and whereinthe third electrode is positioned below the second electrode; a hollowcathode emitter electrode comprising a plurality of hollow cathodeemitters, wherein the hollow cathode emitters are aligned with theapertures in the first, second, and third electrodes, and wherein thehollow cathode emitter electrode is positioned above the firstelectrode; and one or more RF sources configured to do one or more of(i) generate a plasma above the hollow cathode emitter electrode, (ii)apply a bias to the hollow cathode emitter electrode, (iii) apply a biasto the first electrode, and/or (iv) apply a bias to the secondelectrode.
 21. The apparatus of claim 20, further comprising a rotationmechanism configured to rotate and tilt the substrate support with anaccuracy of about 2° or better.
 22. The apparatus of claim 20, furthercomprising a reflector positioned below the third electrode and abovethe substrate support, wherein the reflector is operable to neutralizeions passing through the apertures in the first, second, and thirdelectrodes during etching.
 23. The apparatus of claim 20, wherein atotal gas conductance through the hollow cathode emitters of the hollowcathode emitter electrode is about 10,000 L/min or less.
 24. Theapparatus of claim 23, further comprising a gas by-pass pathway thatprevents formation of an excess pressure differential across theelectrode assembly during times of high gas flow or during pump down.